The invisible minority: why do textbook authors avoid people with disabilities in their books?

ABSTRACT Representation of disability in school textbooks may influence pupils’ knowledge and perceptions of people with disabilities. The aim of this study was to investigate representation of people with disabilities in school textbooks. The study employed a mixed-methods approach. Quantitative frequency analysis was used to investigate the extent of representation of disabilities in texts and pictures in 78 Norwegian textbooks for Grades 5–10. Regarding texts, the results showed that people with disabilities were represented in less than half of these textbooks (49%). Concerning pictures, people with disabilities were even less represented, appearing in only 29% of the textbooks. These quantitative findings were supplemented by a qualitative survey of textbook authors, who were asked to explain the marked absence of disability references in their own books and in school textbooks in general. The two most frequent explanations were that textbook authors had either overlooked people with disabilities, or that the Norwegian National Curriculum (Kunnskapsdepartementet 2006. Lærerplanverket for Kunnskapsløftet (LK06) [The Norwegian National Curriculum]. https://www.udir.no/lk20/overordnet-del/) did not explicitly mention this minority. We discuss these explanations as expressions of conscious considerations rather than unconscious omissions.


Introduction
Inclusive schooling has been on the international political agenda since the Salamanca Statement, which called for the inclusion to be the norm (UNESCO 1994). The UN Convention of the Rights of People with Disabilities (UNCRPD 2006) strengthened this movement towards the inclusion of people with disabilities. Article 24 of the convention specifically recognises the right to inclusive education for people with disabilities. However, a clear gap has been noted between good intentions and actual classroom practices (Powel 2013). In Norway, most pupils receive whole class instruction, even those who also receive special education. As in many other countries, Norwegian pupils with different disabilities are physically included in both ordinary schools and classrooms (Education Act 1998). However, recent investigations have concluded that pupils' everyday experiences of inclusion are often not in accordance with good intentions (Barneombudet 2017;Nordahl et al. 2018). Research Question 1 raises in this article is whether Norwegian school textbooks reflect a diverse classroom by including people with various disabilities. Research Question 2 focuses on the occurrence of absence of people with disabilities in textbooks from the perspectives of the textbook authors.
Already from early childhood, we construct our own understandings of human diversity. Such constructions emerge directly, through interpersonal interactions, and indirectly, through exposure to diverse people in print and other media (Martinez-Bello and Martinez-Bello 2016; Ostrosky et al. 2015). School textbooks in particular are significantly influential because every child is exposed to them during their school years, and as such, they serve as a common reference point (Oates 2014). The importance of disability representation in textbooks is twofold. First, all pupils, including pupils with disabilities, must be able to recognise themselves in their learning materials (Blaska 2003). Adequate representation in textbooks might positively influence their self-image and motivation (Cheng and Beigi 2011). Second, representation is important because of its potential to influence peer attitudes (Ostrosky et al. 2015). Knowledge regarding the attributes and challenges associated with being disabled can potentially contribute to both understanding and breaking down prejudices (Cheng and Beigi 2011). This, in turn, can mitigate or outright diminish the stigmatisation of people with disabilities (Varughese and Luty 2010). It is worth noting that negative consequences can also result from textbook representations of people with disabilities. This might occur, for example, when people with disabilities are represented negative and/or in a stereotypical way (Hodkinson 2016;Price et al. 2016).

Norwegian textbooks
At an overall level, it is the Norwegian National Curriculum (Kunnskapdepartementet 2006) that forms the foundation and framework for education in Norwegian schools. The curriculum is a regulation of the Education Act (1998) and governs the content of education ). A textbook intends to be an operationalisation of the curriculum, and both teachers and textbook authors largely agree that textbooks must adhere to the guidelines given in the curriculum (Bachmann 2004).
In Norway, we do not have a national approval system to ensure that the content of textbooks follows the current curriculum. Publishers, authors and professional fellowships themselves ensure this quality control (Bratholm 2001). This is called a 'deregulated textbook system' . Norway and Sweden have transitioned from state-regulated systems to deregulated systems without state approval during the last two decades , whereas other countries, like Portugal, have changed in the opposite direction, towards a state-regulated system. In practice, the choice of today's textbooks in Norway and Sweden is made by the local educational authority, individual school, teacher or subject section. However, research shows that there is a lack of clear criteria, formality and awareness surrounding the choice of textbooks in Norway (Skjelbred 2003;Bueie 2002).
The textbook is an important learning resource, and teaching practices are largely linked to textbooks in Norway when it comes to planning and implementing teaching (Blikstad-Balas 2014). Textbooks are important for determining which topics are selected, how teachers present the material and which student activities are selected (Bachmann 2005).

What is disability?
Different theoretical models exist when it comes to understanding disability. In chronological order, the following three models are described by Bhaskar and Danermark (2006): medical, socio-economic, and cultural. First, according to the medical model, disability is associated with an impairment located in the body. Second, the socio-economic model holds that disability is a consequence of barriers in the environment. Finally, the cultural model, inspired by post-modernism, is occupied with how normality is conceptualised in different societies. In this model, values and attitudes are amongst the most important mechanisms related to disability. Bhaskar and Danermark (2006) criticise each of these models for being reductionist because they focus on just one or a few levels of reality. Cultural disability research as a post-structural approach is criticised by Shakespeare (2014) for its 'fascination with theory for its own sake' (71) and for being anti-empirical, as opposed to a critical realist approach to the world, as proposed by Bhaskar and Danermark (2006), Danermark and Gellerstedt (2004), and Stylianou (2017) and Wilkinson (2014).
According to critical realism, phenomena in the real world occur in laminated systems (Bhaskar 1975;Bhaskar and Danermark 2006). This means that all phenomena constitute a multiplicity of mechanisms associated with different levels of reality: physical, biological, psychological, psychosocial and emotional, socio-economic, cultural and normative (Bhaskar and Danermark 2006). We agree with the critical realism view suggesting that disability is best understood as an interaction between these different levels. This view is in accordance with the United Nations' Convention on the Rights of Persons with Disabilities' (UNCRPD 2006, 1) definition: 'Disability results from the interaction between persons with impairments and attitudinal and environmental barriers that hinder their full and effective participation in society on an equal basis with others'. It is significant that impairment is included as one of three factors that contribute to hindering people's participation in society (impairment, attitudinal barriers and environmental barriers). Despite the fact that this definition stresses the interactional view of disability, empirical investigations sometimes operate on one level at a time (Bhaskar and Danermark 2006).
We respect the inclusion arguments against categorisation based on impairments from prominent scholars (Florian 2013;Thomson 1997). However, for empirical (methodological) reasons, we distinguish between people with and without disabilities and between various types of impairments. In this respect, we follow the categorisation of disabilities made by UNCRPD (2006, 4): people with physical, mental, intellectual or sensory impairments. The Norwegian Federation of Organisations of Disabled People (https://ffo.no/Organisasjonen/About-FFO/) holds an interactional view of disability. However, instead of interactions between individual and societal elements, they use the wording, 'conflict between the individual's preconditions and society's demands for functioning in areas that are essential for human independence and social existence'. Both the definition from UNCRPD and The Norwegian Federation include individual levels of reality. In accordance with critical realism, they also include socio-economic and cultural levels of reality, for example, various social and cultural barriers, to have a more complete understanding of disability.
As mentioned above, we use the term disability in accordance with the critical realist view and the UNCRPD (2006) definition. Based on these and similar definitions, people with disabilities constitute about 15% of the population, both nationally (Molden and Tøssebro 2009) and internationally (World Health Organization 2011). People within this minority group are amongst the most stigmatised people in the world because of their invisibility and a general lack of knowledge and understanding about them (UNICEF 2013). We argue that it is of great importance to make such a large minority group more visible in the curricular materials used in schools. However, we also recognise the argument against such visibility because of the danger of highlighting their differences, rather than their similarities, with non-disabled pupils (Florian 2013).

Representation of disability in school textbooks
There are several studies exploring portrayals of disability in classic children's literature (Beckett et al. 2010). However, there are relatively few studies reporting representation of disabilities in school textbooks, and if represented at all, it is a limited number of them (Reichenberg 2017). For example, people with disabilities were included in only 1.5% (24 of 1600 books) of children's books used in American kindergartens, primary schools and special education programmes (Blaska 2003). This percentage is similar to Hardin and Hardin's (2004) finding about the prevalence of depictions of people with disabilities in general physical education textbooks. Worse, in about three-quarters of the cases, children with disabilities were depicted as needing support. Both text and pictures from 494 electronic resources used in primary schools in England, including digital textbooks, were analysed by Hodkinson (2012). Surprisingly, only a single digital textbook referred to disability directly.
In a Columbian study of pictures in early childhood textbooks (Martinez-Bello and Martinez-Bello 2016), only two of the 533 images of children in these textbooks showed someone with a disability. In another non-Western society, Iran, Cheng and Beigi (2011) found that textbooks in English for Iranian Foreign Learners seldom represented disabilities in text and pictures.
Two overall findings from the research on disability representations in media and text should be particularly emphasised (Favazza et al. 2017;Hodkinson 2012): (1) the appearance of disability in books written for children, including textbooks, is restricted; and (2) people with disabilities are often presented in a negative and stereotypical way in children's literature.
Little attention has been paid to the subjects in which disabilities are represented in textbooks. However, it seems that disability is more commonly depicted in textbooks used in physical education (PE) than in textbooks for most other subjects. For example, an investigation of illustrations in 17 Spanish PE-textbooks for secondary education found that of 256 pictures randomly selected from the total number of illustrations, 10% showed people with disabilities (Vidal-Albelda and Martinez-Bello 2017). This percentage is higher than what we found in textbook analyses from research that did not report which subjects the books represented.
In the Norwegian school context, we found no studies reporting on the representation of disability in textbooks. However, in the Swedish school context, which is comparable with the Norwegian context (Reichenberg and Andreassen 2018), a study analysed the representation of disability and people with disabilities in 30 textbooks covering history, social studies, science and religion for Grades 6-10 (Reichenberg 2017). The results showed that 13 of these textbooks (43%) included no representation of disability, neither in text nor in pictures. For the remaining textbooks, people with physical disabilities were more frequently represented than those with mental disabilities, and they were mostly presented as active participants in society. This finding confirms the conclusion about the shift towards more positive and inclusive representations, at least in Western society (Hodkinson 2016). What is still missing, however, is an analysis of why so many textbooks still seem to avoid people with disabilities. Our study contributes to this lack of research.

Theoretical approaches to the absence of disabilities in textbooks
In this article two approaches have been used to explain the absence of disabilities in textbooks. The first is the critical realist view of the absent curriculum, as proposed by Wilkinson (2014). The second is Thomson's extension of Douglas' (1966) theory on cultural intolerance against the extraordinary.
Critical realist view of the absent curriculum Based on critical realism, Wilkinson (2014) discusses the concept of the absent curriculum as 'the totality of the curriculum that could have been but has not been taught' (420). He divides the absent curriculum into three component parts or levels: (1) the absent null curriculum; (2) the absent unselected curriculum; and (3) the absent unenacted curriculum.
The first one operates at the level of national policy and is comprised of topics that could have been but are not included in the formal curriculum. The second part operates at the school level and is comprised of topics that are available but have not been selected by the school-based curriculum. The third part operates at the classroom level and is comprised of topics within topics that are available for teaching but are not taught in the classroom. We propose that textbooks are operationalisations of not only the present curriculum (Bachmann 2004), but also the absent curriculum (Wilkinson 2014, 420). In the case of textbooks as a curricular substitute, all component parts/ levels of absence could be relevant.
Negative emotional and learning impacts of curricular absence from certain cultural contributions, are investigated for children from cultural minorities (Wilkinson 2014). This research indicates that absence is not just indeterminate nothingness; it also has a significant effect on pupils' learning. We argue that similar negative impacts for pupils with disabilities could be the case for the absence of people with disabilities in textbooks. We argue that absence may also affect peers' attitudes towards the inclusion of people with disabilities.

Thomson's extension of Douglas' theory on cultural intolerance
We suggest that Thomson's (1997) extension of Douglas' theory on cultural intolerance informs the understanding of absence of people with disabilities in textbooks (Douglas 1966). Thomson (1997) discusses five strategies in which Western culture has handled people with disabilities (in Thomson's terminology; 'extraordinary bodies') and the threat of being different. We concentrate on two of them. The first strategy is to make people with disabilities invisible. This corresponds with the view of disability studies from a cultural and literary perspective. Traditionally, the lived experiences of people with disabilities have been discredited or ignored. Among several conditions, this group has been isolated, incarcerated, observed, instructed, regulated, treated, institutionalised and controlled to a degree, probably unlike what other minority groups have experienced (Davis 2006). From a classic literary perspective, people with disabilities have been rendered societally invisible, being under-theorized compared to other group theories like multiculturalism, feminism and class (Davis 1995). 'Narrative prosthesis' indicates that literature through history has used disability as a crutch upon which narratives lean for their representational power, disruptive potentiality and analytical insight (Mitchell and Snyder 2000). Sometimes people with disabilities are presented as 'unique'. If people with disabilities are presented in a prominent way, it is often used as a symbol or for comparative purposes (Mitchell and Snyder 2000). In short, according to Mitchell and Snyder (2000), disability in narrative is both excessively visible and conversely invisible.
Invisibility was most egregiously expressed in the eugenics movements in 1930s United States and Europe, via legislation that allowed for the sterilisation of people with mental disabilities. Today, foetal diagnostics have made it possible to identify and remove a foetus with physical or mental anomalies. Such practices can be regarded as an advanced form of elimination.
The second strategy that we adopt from Thomson (1997) is to handle people with disabilities by preventing the society from being exposed to them. Thomson (1997) pointed out how the United States had legislation in the 1900s that forbade visually disabled people from appearing in public places. At the same time, in Norway, large central institutions were established to house people with intellectual disabilities, thereby separating them from Norwegian society at large. Their housing, work training, and education all took place within these institutions. Therefore, the surrounding society hardly recognised that these people existed. Thomson use the terms inclusive world building and eugenic world building to express two contradictory initiatives which are expressed in modern society (Thomson 2017). These two initiatives entail inclusion and exclusion of disability, respectively.
To further investigate the representation and absence of people with disabilities in textbooks used in an inclusive learning environment in which the Norwegian school system agree upon (UNCRPD 2006;UNESCO 1994), we investigated the following research questions: 1. To what extent are people with disabilities represented in Norwegian textbooks for Grades 5-10 on the subjects of Norwegian language and literature, religion, science and social studies (geography, history and sociology)? 2. What are the textbook authors' explanations for the absence of people with disabilities in many Norwegian textbooks?

Methodology
A two-phase, mixed methods study was undertaken to illuminate the occurrence of representation and absence of people with disabilities in Norwegian school textbooks. The quantitative first phase was followed by a qualitative second phase intended to explain the quantitative results. This is referred to as an explanatory sequential design (Creswell and Creswell 2018). The first phase was intended to answer Research Question 1: To what extent are people with disabilities represented in Norwegian textbooks for Grades 5-10 on the subjects of Norwegian language and literature, religion, science and social studies? To investigate this question, we used quantitative frequency analyses based on a sample of elementary and lower secondary school textbooks. These school levels were chosen because textbooks play an especially prominent role in directing teaching at these levels (Skjelbred et al. 2017). Based on the results of the Research Question 1, the second phase of the study comprised a digital survey with open-ended questions sent to all the textbook authors of the school textbook samples analysed in Phase 1. The subsequent qualitative content analysis (Schreier 2014) of these survey data was aimed at answering Research Question 2: What are the textbook authors' explanations for the absence of people with disabilities in many Norwegian textbooks? Content analysis is the interpretation of the content of text data through the systematic process of coding in mutually exclusive categories. This is opposed to discourse analyses which is interested in examining people's linguistic repertoires and how these are linked to different representations in context.

Phase 1
Related to Research Question 1, we requested that the four largest textbook publishers in Norway (Gyldendal, Cappelen Damm, Aschehoug and Fagbokforlaget) send us their most-sold and valid sample textbooks for Grades 5-10 during the past two years. We chose these grades because from Grade 5 on, pupils are supposed to use readings from textbooks as their primary learning tool. We chose the following subjects: Norwegian language and literature, religion, science and social studies (in Norway, social studies are consisting of the subjects of geography, history and sociology). We chose these subjects as they were likely to describe or illustrate human diversity, either as part of the subject's distinctive character or as a natural means of reflecting diversity. In total, we received 78 textbooks published between 2010 and 2018. The number of books in the sample was distributed amongst the different subjects as follows: Norwegian language and literature (25), religion (10), science (13), geography (9), history (9), sociology (8) and social studies (4). This distribution corresponds to the approximate time distribution between the different subjects according to the Norwegian National Curriculum (Kunnskapsdepartementet 2006). The process of the textbook analysis began by distributing the 78 books amongst the three researchers to read carefully and focused, page by page, on searching for representations of people with disabilities. Every representation was registered according to a coding scheme containing the following categorisation: presentation form (picture or text), textbook subject (Norwegian language and literature, religion, science and social studies) and disability (physical, mental, intellectual or sensory). This categorisation of disability was in accordance with UNCRPD (2006). They also emphasise that disability is of a persistent nature, for example, blindness or a developmental disability such as autism. A representation of a person with a bone fracture, for example, would in this case not be considered a finding. A further coding criterion was that the disability should either be mentioned by its name (e.g. a diagnosis), or else that it should be described in a way that clearly indicates a disability. Codes were entered into the Statistical Package for the Social Sciences (SPSS) for frequency analyses.

Phase 2
In the follow-up qualitative research phase, related to Research Question 2, we investigated the textbook authors' explanations of why people with disabilities were absent in many school textbooks. Using the digital tool SurveyXact, we developed an anonymous survey questionnaire. In addition to requesting demographic data, the questionnaire posed three open-ended questions: (1) 'What do you think are the explanations for why people with disabilities are often omitted from Norwegian school textbooks?' (2) 'What are the reasons/arguments for including/not including texts or pictures of people with disabilities in the textbooks to which you have contributed?' (3) 'When it comes to your field of study (your subject), is there something in its content that suggests that people with disabilities should be represented in school textbooks'? We point out that the term disability was explained to the textbook authors in accordance with UNCRPD's (2006, 1) definition.
E-mail containing an invitation and a link to the questionnaire embedded, was sent to all 73 textbook authors of our textbook sample (78 books). They were encouraged to reply within two weeks. A reminder was sent three days before the deadline.
We received 24 completed surveys. Our analysis of the answers from the questionnaire followed methodological suggestions about qualitative content analysis (Schreier 2014). By coding the answers from the first survey question manually, the three authors cooperated in building a trial-coding frame. In this coding frame, explanations for the absence of disabilities made up the primary category. Each answer constituted a unit of analysis and consisted of one or more explanations for absence. Based on thorough cooperative reading and discussion of each unit of analysis, we inductively generated five mutually exclusive subcategories of explanations/arguments for absence: 1. Disability was overlooked by textbook authors (unconscious omission). 2. Textbook authors did not find disability explicitly mentioned in the Norwegian National Curriculum. 3. Textbook authors struggled to find good texts about disability. 4. Textbook authors found disability to be irrelevant to their subject(s). 5. Textbook authors considered disability to be a sensitive/difficult topic.
The second survey question asked the textbook author about their reasons for either including or excluding disability in their textbooks. The answers did not reveal any new explanations for or arguments against including disabilities or people with disabilities in textbooks, as compared to the answers given to the previous question in the survey. Therefore, no new subcategories were added.
The third survey question asked whether the content of the textbook authors' fields of study suggested that disabilities should be represented in school textbooks. Although this was essentially a yes/no question, some of the answers given by textbook authors were elaborate and argumentative. In our analysis, we subcategorised the answers dichotomously, coded as 'yes' or 'no'. The second and the third survey question did not directly correspond to either of the two research questions but were rather used to illuminate and discuss the results regarding Research question 2.

Limitations
Some limitations of this study should be addressed. The sample, for instance, was restricted in terms of which subjects were included and with respect to grade levels. Moreover, the publishers themselves selected and sent us the textbooks that, in their opinion, were the most frequently used in Grades 5-10 in the past two years. Naturally, these considerations warrant caution when attempting to generalise the results of this study. The study was also limited to the Norwegian context. To our knowledge, no similar research about textbook authors' explanations for absence has so far been conducted, which in turn gave us no direct basis for comparison of our results.
Only about one-third (24 of 73) of the textbook authors who were contacted responded to the survey. This could represent a threat to the reliability of our results. Another limitation concerns ecological validity: We do not know how teachers use texts and pictures of people with disabilities in their classrooms. Therefore, we also cannot know how pupils with and without disabilities perceive these texts and pictures.

Results
Below, the results are presented in accordance with the research questions.

Research Question 1
To what extent are people with disabilities represented in Norwegian textbooks for Grades 5-10 on the subjects of Norwegian language and literature, religion, science and social studies (geography, history and sociology)?
Via quantitative frequency analysis, our findings are reported for texts (Table 1) and pictures (Table 2) separately. Table 1 shows that people with disabilities are represented in the texts of 38 of the 78 sampled textbooks. The amount of textual representation differs from subject to subject, with history having the highest prevalence (6 of 9) and sociology having the lowest (1 of 8). In the subject 'Norwegian language and literature', which had the largest number of textbooks in our sample, we found disability represented in 13 of 25 textbooks. Moreover, Table 1 shows that physical and sensory disabilities are represented in the texts of 27 of the 78 sampled textbooks, while mental and intellectual disabilities are represented in the texts of 22 of the textbooks. Table 2 shows that people with disabilities are represented in pictures in 23 of the 78 textbooks, although the percentage of representation differs from subject to subject. Science textbooks have the highest percentage of representation of disability in pictures (7 of 13 textbooks). Geography textbooks, on the other hand, had no pictures of disability. Table 2 shows that physical and sensory disabilities are represented in pictures in 20 of the 78 textbooks. Although social studies for primary school (2 of 4) had the highest percentage, it must be noted that this equates to only four textbooks in total.
Beyond the findings outlined in the tables, Norwegian language and literature featured more text on mental and intellectual disabilities than the other subjects.

Research Question 2
What are the textbook authors' explanations for the absence of people with disabilities in many Norwegian textbooks?
Based on the content analysis of the answers to the first survey question, 'what do you think are the explanations for why people with disabilities are often omitted from school textbooks?', we made the following subcategorisation of the textbook authors' explanations for absence, with the number of findings within each subcategory in brackets: 1. Disability was overlooked by textbook authors (unconscious omission) (9). 2. Textbook authors did not find disability explicitly mentioned in the Norwegian National Curriculum (9). 3. Textbook authors struggled to find good texts about disability (6). 4. Textbook authors found disability to be irrelevant to their subject(s) (6). 5. Textbook authors considered disability to be a sensitive/difficult topic (4).
Below, each explanation is illustrated by a direct quote from a textbook author. The quotes were carefully translated from Norwegian to English to preserve their intended meaning.  According to the categorisation above, the two most frequent explanations for the absence of disabilities were unconscious omission and absence from the curriculum. As outlined above, nine textbook authors claimed that absence was caused by unconscious omission. As one author wrote: Actually, I have never thought about them (people with disabilities) as not being represented, or that we had never talked about it (disabilities) when working with the books. (ID 23,religion, An equal number of textbook authors (9) referred to the Norwegian National Curriculum to explain the absence of disabilities. They claimed that disability was absent from the curriculum and was therefore not an essential topic in the textbooks. As one author stated: Textbook content follows from the curriculum. The publishers are extremely obsessed with this [in order] for the books to be sold. (ID 3, science, Grades 5-7) Some authors claimed that disabilities or people with disabilities have never been mentioned in any subject curricula. 1 However, one religion textbook author stated that the curriculum should not be used as an argument against disability representation: The curriculum mentions equality, gender equality and human rights, and therefore we who have designed the textbooks should have had the imagination and willingness to consider this dimension, which is so important to many people. (ID 5,religion, The third most frequent explanation for the absence of disabilities in many textbooks was the difficulty involved in finding good texts about this topic. Norwegian language and literature authors, in particular, used this explanation. 2 As one remarked: There may exist few good texts about these groups of pupils (with disabilities) that textbook authors can use; therefore, they have to write [them] themselves, which they have no competence for. (ID 19,Norwegian, Most of the six authors in this subcategory mentioned that absences in textbooks reflected the widespread absence of disabilities in children's books in general. The next explanation, also given by six textbook authors, was that they did not find disability to be a relevant topic for their textbooks, with several authors arguing that its relevance depended on the subject theme. As one author (ID 13, science, Grades 8-10) said, 'if disabilities are not relevant to the theme, it may seem imposed on to write about it … ' It seemed that they did not consider disability to be part of their subject.
The last subcategory, as explained by four authors, was that disability is a sensitive or difficult topic to address in textbooks. These authors were fearful of misrepresenting people with disabilities and/or offending or further stigmatising pupils with disabilities. One of these authors (ID 4, sociology, Grades 8-10) added that 'this has been a taboo theme'.
In the second survey question, we asked the textbook authors about their arguments for including/not including text or pictures of disabilities and people with disabilities in their own textbooks.
Their answers to this question, which focused on the textbook authors' own publications, did not reveal any new explanations for or arguments against including disabilities or people with disabilities in textbooks, as compared to the answers given to the previous question in the survey. However, several textbook authors generally referred to reasons for including representations of disability in both text and images without having actually included anything about disability in their own textbooks. Only six textbook authors related their reasons for including disability in their own textbooks.
In the third survey question, we asked the textbook authors whether the content of their subject area gave cause to represent people with disabilities in the textbooks. All but three of the textbook authors believed people with disabilities were relevant to their subject area and should be mentioned. As one of the authors explained: Children and youth should gain insight into other people's lives and living conditions. That's why it's important to meet and read about people in different situations and with different disabilities. In this way, pupils will develop an understanding, insight and commitment to the diversity amongst us. (ID 20, Norwegian, Grades 5-7)

Discussion
This study investigated two research questions. Research Question 1 was about the extent of representation of people with disabilities in Norwegian textbooks for Grades 5-10. We found a substantial lack of representation in our textbook sample. Approximately one-half of the textbooks had no textual representations, while two-thirds of the textbooks had no representations in pictures. Mental and intellectual disabilities were less frequently represented in either text or pictures than were physical and sensory disabilities. This finding could be due to the implication that physical disabilities are easier to depict (Reichenberg 2017; Vidal-Albelda and Martinez-Bello 2017). Although absence of people with disabilities seemed to be more uncommon in our study than in previous studies in other national contexts (Blaska 2003;Hodkinson 2012;Martinez-Bello and Martinez-Bello 2016), representations were absent in more Norwegian textbooks than in Swedish textbooks (Reichenberg 2017). In conclusion, our study confirmed the findings of other studies that people with disabilities are absent in far too many school textbooks.
Research Question 2 addressed the explanations given by textbook authors for the absence of representations of people with disabilities in many textbooks. The two most frequent explanations were that (1) disability was overlooked (unconsciously omitted), or that (2) disability was consciously omitted because it was not explicitly mentioned in the Norwegian National Curriculum. The latter explanation, however, is not in line with reality. When taking the content of the entire curriculum into consideration, disability is mentioned, namely in the core curriculum. This argument, together with the three remaining arguments (17), reflect conscious considerations from the textbook authors, whereas the first reflects unconscious omission. Moreover, we also found that most textbook authors indicate that representations of people with disabilities are relevant to their subject area and should therefore be included in the textbooks. This is contrary to the finding that they still exclude disabilities in their own textbooks. This contradiction strengthens the belief that absence is a default practice within the textbook tradition (Davis 1995).
Such a default position is compatible with Thomson's extension of Douglas' theory about cultural intolerance against the extraordinary (Thomson 1997;Douglas 1966). In this theory, omission is one of several strategies by which society asserts order against the extraordinary. In particular, the second strategy (Thomson 1997), which is to prevent so-called 'ordinary people' from being exposed to the extraordinary, coincides with the textbook tradition of omitting disability from textbooks (Blaska 2003). As such, the absence of disabilities could be the result of a long-standing (and ongoing) process of omission. People with disabilities are often made symbolic or mysterious factors in the literature, but are rarely portrayed as what they are, making the disability invisible (Mitchell and Snyder 2000). Thomson (2017) points out that when disability is presented either in picture or text, it both presents a challenge and an opportunity for solutions of how people with disabilities are represented in an inclusive way into the society. In contrast to what Thomson (2017) calls eugenic world building and the cultural intolerance against the extraordinary, she promotes an understanding called inclusive world building. This view is consistent with the UNCRPDs (2006) understanding of disabilities, and claims that disabilities is an essential characteristic of being human and gather us into the everyday community of embodied humankind. Inclusive world building frames disability as a valued social diversity and seeks to integrate people with disabilities into it by creating an barrier free environment. When representation of people with disabilities is totally absent in many school textbooks, this opportunity and even challenge to represent people with disabilities in an inclusive way is deprived, and rather contributes to exclusion and invisibility for this minority group in school textbooks.
Concerning our findings of explanations reflecting textbook authors' conscious considerations leading to absence, one refers to the difficulties encountered when trying to find appropriate texts about disabilities, while another refers to disability as a sensitive topic. Both of these explanations demonstrate that textbook authors are aware that disability categorisation is negatively charged. Categorisation is the initial way by which society handles disabilities (Davis 1995;Thomson 1997;Davis 2006). Being assigned to a certain category promotes thinking about being or not being included in society. An awareness of such thinking could reinforce some textbook authors' decisions to omit representations of disabilities in their textbooks. To promote thinking of inclusion, one solution is to incorporate people with disabilities into ordinary society as 'one of us'. According to Thomson (1997), this is the only positive way to handle disability. This positive view corresponds with Norwegian and international intentions of inclusive education (Kunnskapsdepartementet 2006;UNESCO 1994UNESCO , 2015UNCRPD 2006). Our results show that only about one-half of the textbook authors considered such inclusive intentions to be reflected in their textbooks. This does not necessarily mean that the absence found in the other half of the textbook sample is due to exclusionary attitudes towards people with disabilities. This could simply be due to their conscious considerations about the negative consequences of categorisation and/or to their opinion that no representation is better than negative representation.
Textbooks are operationalisation of both the present curriculum (Bachmann 2004), and the absent curriculum (Wilkinson 2014). The absent curriculum emphasises the meaning of what is not there, themes that are not presented and remains left out also communicates with its absence. When people with disabilities are excluded from textbooks, the absents itself can be understood as a possible barrier to promote an inclusive learning environment.

Implications for practice and further research
The finding that people with disabilities are excluded and made invisible in many textbooks is worrying for several reasons. In particular, school textbooks can potentially influence all children, because every child is exposed to them during their school years. The content of textbooks is also important for what is further thematised and discussed in the classroom and can thus contribute to increased knowledge and inclusion in the field. It is also important that textbooks reflect the diversity of the population so that all pupils have the opportunity to recognise and identify with good role models in their school's learning materials (Blaska 2003). Furthermore, this may have an impact on the development of inclusive attitudes and on inclusive practices in society in general (Ostrosky et al. 2015).
For these reasons, textbook authors have an important social responsibility with respect to decisions made about what should be included in textbooks and how human diversity should be represented. It is troubling that so many textbook authors explained that the reason for their exclusion of the world's largest minority group from textbooks was unconscious omission.
There is undoubtedly a need for increased focus and attention in this area to secure the representation and inclusion of people with disabilities. At the same time, it is important to focus on the ways in which people with disabilities are represented in order to avoid negative or stigmatising representations. It is unfortunate that people with disabilities are often made visible simply because of their disability, as this highlights the differences rather than the similarities between people.
It is also clear that textbook authors are largely guided by the Norwegian National Curriculum (Kunnskapsdepartementet 2006) when making decisions about what to include in textbooks. In this context, the responsibility for making people with disabilities visible is elevated to a national level. It is a national responsibility to ensure that the diversity of the entire population is reflected and represented in an inclusive way through public and governing documents as a curriculum. Notes 1. The Norwegian Curriculum for Compulsory School consists of three parts. First, there is the Core Curriculum; second, the Quality Framework; and third, the Subject Curricula. 2. Especially in this subject, the authors are both writers and editors of their textbooks; as such, they often include excerpts from children's literature in their textbooks.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Notes on contributors
Magne Skibsted Jensen is an associate professor of pedagogy in the Faculty of Teacher Education at Østfold University College, Norway, where he is a member of the research group Special Education. He also works in Teacher Education, where he leads projects including new approaches of practice training. Skibsted Jensen´s research focuses on pre-service teacher education, special education and mentoring. His research interests include dyslexia, self-regulated learning, study strategies, study motivation, inclusion and mentoring in professions.
Marte Herrebrøden is an assistant professor in the Faculty of Teacher Education at Østfold University College, Norway, where she is a member of the research group Special Education. She teaches courses in special education and basic pedagogy. Her research interests are related to children's mental health in general and school settings in particular, children with social and emotional challenges, neurodevelopmental disorders and school refusal.
Ulf Rune Andreassen, PhD, is a professor of Special Education in the Faculty of Teacher Education at Østfold University College, Norway, where he is a member of the research group Special Education. He is the coordinator of the Master program in Special Education. His research focuses on inclusive education, reading comprehension, reading disability, students' and teachers' selfefficacy.