Proceso de Estandarización de Compuestos Primarios

As mentioned previously (page 35), most researchers now conceptualise RRB as a multi-dimensional construct, but there is not universal agreement upon the precise sub-groups of RRBs. The DSM-5 (APA, 2013) divides RRBs into: stereotyped and repetitive speech, motor movements or use of objects; adherence to routines, rituals and resistance to change; restricted and circumscribed interests; and hyper- and hypo- sensory responsivity and unusual sensory interests. The ICD-10 (WHO, 1993) also sets out four sub-categories which are: motor stereotypies; preoccupations with parts of objects; CI; and adherence to routines. These generally map onto one another, with the exception of the DSM-5’s sensory category and the ICD-10’s preoccupations with parts of objects. As mentioned previously, RRBs have also been divided in to higher- and lower-order RRBs (e.g. Prior & Macmillan, 1973; Turner, 1999a). However, it can be conceptually difficult to categorise individual RRBs as either a higher- or lower- order behaviour. For example, preferring to wear the same clothes may stem from a desire to maintain sameness, or it could be because other clothes cause sensory discomfort.

Several researchers have attempted to identify the sub-categories of RRB using statistical methods, specifically exploratory or confirmatory factor analysis (EFA or CFA) and PCA. EFA and PCA are used to express datasets arising from measures that

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comprise numerous variables as a smaller number of factors or components made up of inter-correlating items (Kline, 2000; Tabachnick & Fidell, 2014). They are an

empirical method for determining the number and composition of a construct’s sub- categories, as well as assessing conceptual and construct validity (Briggs & Cheek, 1986; Shuster et al., 2014; Williams, Brown & Onsman, 2010). Running these analyses results in a series of factor loadings for each item on each identified factor, which indicate how strongly the item is correlated with the factor (Kline, 2000). They are particularly useful for assessing measures of phenomena that are not directly

observable; as is the case for IS behaviours. The range of different factor solutions of RRBs in participants with ASD found across studies is displayed in Appendix 2 (Table 8.2, pages 243-249).

The majority of studies (N=17 [63%]) investigating the structure of RRBs in ASD have identified two sub-groups; one comprising RSMBs such as pacing, hand flapping and rocking, and the other comprising more abstract behaviours such as routines and CI, which are collectively referred to as insistence on sameness (IS; e.g. Bishop et al., 2013; Cucarro et al., 2003; Honey et al., 2012; Lidstone, Uljarević et al., 2014; Richler et al., 2010), although the precise naming of factors may vary slightly between research groups. This binary grouping has also been found in studies of TD children (e.g., Evans et al., 1997; Leekam et al., 2007).

However, this is not always the case. Other studies have identified alternative solutions comprising three (Honey et al., 2008; Lam, Bodfish, & Piven, 2008; Mirenda et al., 2010), four (Anagnostou et al., 2011) or five factors (Bishop et al., 2013; Lam & Aman, 2007; Mirenda et al., 2010; Scahill et al., 2014). In the case of three factors, these usually comprise factors equivalent to RSMB and IS, along with an additional factor equivalent to CI (e.g. Honey et al., 2008; Lam et al., 2008) or self-injury factor (Mirenda et al., 2010). There is somewhat more variety within the solutions of four or more subgroups, however they generally map on to the four DSM-5 categories, and may include self-injury (e.g. Bishop et al., 2013; Lam & Aman, 2007; Mirenda et al., 2010; Scahill et al., 2014); with the notable exception of Bourreau, Roux, Gomot, Bonnet-Brilhault, and Barthélémy (2009) who identified four factors equivalent to RSMB and IS and two epiphenomenal factors.

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Such differences are likely due to the use of RRB measures that are different in terms of their scope and format; I have already discussed the difficulties of comparing across measures in the previous section. The largest proportion of studies (N=14 [52%]) use the ADI-R (e.g. Bishop et al., 2013; Mooney et al., 2009; Shao et al., 2003). All of these studies demonstrate two sub-groups, RSMB and IS, with two exceptions (Honey et al., 2008; Lam et al., 2008). The next most common measure is the RBS-R questionnaire, used in four studies (e.g. Lam & Aman, 2007; Mirenda et al., 2010). Although the RBS-R was conceptually designed with six sub-scales, factor analysis generally results in five sub-scales; although Mirenda et al. (2010) found evidence for both a three- and five-factor model depending on how the scale is to be used, and Georgiades, Papageorgiou and Anagnostou (2010) found two subscales in the Greek version of the RBS-R. Comparing just these two measures, the RBS-R covers a much wider range of behaviours than the ADI-R, which may account for the difference between factor solutions. Most of the factor analysis studies have been conducted on interview/questionnaire measures, with one exception; Bourreau et al. (2009) devised a measure based on observation, supplemented by parental report, the Restricted and Repetitive Behaviour Scale.

As mentioned, there is disagreement over whether or not certain behaviours should be included as RRBs. For example, the RBS-R includes several items on self- injurious behaviours, which may explain why a separate self-injury sub-scale emerges, whereas there is just one self-injury item in the ADI-R and no self-injury item in the RBQ-2 (Lidstone, Uljarević, et al., 2014). Even when different research groups use the ADI-R, there may be considerable variation in terms of what items are included. For example, Lam et al. (2008) did not include unusual sensory interests because at the time they weren’t included as part of RRB under the DSM-IV (APA, 2000) and several studies do not include CI as this item is only administered to older children (e.g. Honey et al., 2008; Mooney et al., 2009; Richler, Bishop, Kleike & Lord 2007). There is also evidence that inclusion of different items considerably alters the results; Smith et al. (2009) replicated the usual two-factor model of the ADI-R but found a four-factor model was a better fit when including verbal rituals, which falls under the

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researchers use the current or ever codes for the ADI-R; although Szatmari et al. (2006) used both and found no difference between the solutions.

Another reason for the variety in factor solutions may lie in the nature of PCA and EFA themselves. There are few hard and fast rules when carrying out factor analytic studies, and a number of decisions need to be made that can affect the outcome of the analysis. These decisions include whether or not to carry out EFA or PCA, what method of rotation to apply to the data, how to extract factors and what cut-off to use for item loadings. These issues are discussed in further detail in the following chapter (page 61). The range of different factor analyses and rotation methods alone can be seen from Appendix 2 and may account for some of the differences between solutions. For example, the majority of studies (N=15 [55%]) employ orthogonal rotation only, and N=6 (22%) employ oblique rotation5 _only;

however, 53% (N=8) of studies using orthogonal rotation identify two factors, and 50% (N=3) of studies using oblique rotation identify two factors. Therefore differences in rotation may not explain the difference in number of factors identified.

In summary, there is considerable variation in terms of the factor analytic solutions of RRB, due to the variety of measures and methods used. Most commonly, researchers identify a two factor solution comprising RSMB and IS (or equivalently named factors), which maps on to the conceptual distinction between lower- and higher-order RRBs (Turner, 1999a). This is most strongly supported by the fact CFA using the ADI-R supports a two-factor solution (Richler et al., 2007; Richler et al, 2010). However, most of these studies used the ADI-R, so while it seems that RSMB/IS reflects the genuine structure of RRBs, this may not be the case, and further research using other measures is required. The findings from this review highlight the importance of assessing the factor analysis of the RBQ-2A as part of this thesis; especially given the fact that none of these studies were conducted exclusively with adults. The following section will consider evidence from previous research about the presentation of RRBs in adulthood.

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