Testing the psychometric properties of the illness perceptions questionnaire for OCD (IPQ-O)

The common-sense model (CSM) proposes that our personal understandings of illness are key determinants of how we respond and adjust to health threats [1, 2]. The validity of the CSM has been widely tested through a large body of research in physical health conditions. The development of the Illness perceptions questionnaire (IPQ), and its revised form the IPQ-R, has contributed enormously to this research as these measures enable perceptions about illness to be quantifiably assessed [3, 4]. The IPQ-R assesses two key components of illness understanding posited within the CSM; cognitive and emotional representations of illness, together known as illness perceptions [4]. In the IPQ-R, the main section consists of seven sets of Likert-type scales, which are summed to measure six dimensions of cognitive representations (timeline acute/chronic, consequences, personal control, treatment control, illness coherence, and timeline cyclical) and one emotional representation dimension. The remaining two dimensions of cognitive representations described in the CSM, identity and cause, are measured separately through two individual scales. A meta-analysis of 45 studies testing the CSM in physical health conditions found that illness perceptions were associated with key illness responses and outcomes, such as coping strategies and levels of psychological distress [5].

A growing body of literature has sought to understand the CSM’s utility in mental health conditions. A systematic review found that the dimensions of cognitive and emotional representations applied to mental health conditions and that, as with physical health conditions, these perceptions link to variance in personal response and outcomes [6]. On the other hand, several qualitative studies have cast doubt on the application of the CSM to mental health conditions, for example, in the case of a study on postnatal depression, the authors concluded that understandings of the condition were too complex to fit within ‘neat’ dimensions of understanding [7]. Baines and Wittkowski (6) highlight the need for further qualitative exploration of illness perceptions in mental health, to identify potential, additional categories of perception and to facilitate the adaptation of tools such as the IPQ-R.

Obsessive-compulsive disorder (OCD) is a debilitating mental health condition, with a frequently chronic course and impairing effect on sufferers of the condition [8] and their family members alike [9]. There is a substantial average gap of up to 17 years between symptom onset and receipt of treatment [10, 11], together with high rates of disengagement from efficacious treatments such as psychological therapy [12]. To our knowledge, no study has tested the associations between illness perceptions and these behavioural responses in OCD.

The primary aim of this study was to test the psychometrics of a new version of the IPQ-R, which has been adapted for OCD following preliminary qualitative work [13]. A secondary aim was to examine associations between perceptions of OCD with emotional responses, help-seeking intentions and treatment use. Understanding the relationships between perceptions of OCD and these responses would both provide support for the CSM and suggest ways in which condition management could be enhanced and psychological distress reduced.

Psychometric testing has enabled the development of a reliable and valid measure of illness perceptions, adapted for OCD. Mirroring the format of the IPQ-R, the IPQ-O is made up of three sections: first, the identity scale, which reflects OCD specific symptoms discussed by people with OCD as part of qualitative interviews, second; the main-subscales, consisting of seven dimensions derived from factor analysis and thirdly, the cause sub-scales, made up of four sub-scales identified through factor analysis that represent the views of people with OCD.

The resultant set of main sub-scales included three of the original IPQ-R sub-scales. These three sub-scales (consequences, coherence and the emotional representation) are now validated in an OCD sample. The coherence scale includes all original IPQ-R items, however, the other two sub-scales were made more specific to OCD through the addition of new items. Eight new items supplemented the consequences sub-scale. Amongst these, the strongest loading items reflect negative social consequences of OCD. Two of these items were originally expected to fit with emotional representation items (worthlessness, shame/embarrassment). It is possible that these emotions load together with consequence items as they incorporate elements of social concerns/evaluation to a greater extent than the other emotional representation items (e.g. being afraid, upset, anxious etc.). The emphasis on social impairment within the OCD-specific consequences sub-scale is consistent with the literature. The social domain of quality of life in OCD has been shown to be particularly reduced compared with other mental health or physical illnesses [29]. The retention of an independent emotional representation dimension (supplemented by one ‘new’ item) is noteworthy as it supports the conceptual difference between cognitive and emotional representations proposed by the CSM [4].

Despite support for three of the IPQ-R’s dimensions, the remaining sub-scales highlighted differences in the way people with OCD perceive their condition compared with chronic physical health conditions. Three potential new sub-scales were derived from our previous qualitative study [13]. One of these sub-scales, perceptions of OCD as on a spectrum in the general population, was validated as a distinct sub-scale. Items from the other two proposed sub-scales combined with items from existing IPQ-R dimensions to create new meaning. One of these sub-scales, perceptions of OCD as part of the self, loaded with timeline acute/chronic items, a scale which in the original IPQ-R measures respondents’ beliefs about the illnesses’ chronicity [2]. Though these dimensions were discussed separately within our qualitative findings, the loading together of these items is understandable as the perceived permanence of OCD contributed to participants’ perceptions of the condition as ‘part’ of themselves [13]. There was a sense that OCD was now ‘ingrained’ and that even with treatment, it would only improve but never fully remit. Thus, OCD was accepted as a permanent part of self-identity. We would posit that these items load together because acceptance of OCD as part of the self is an extreme view of illness permanence. Notably, the mean sub-scale score for permanence items was 3.97, demonstrating that the sample endorsed a perception of the condition as permanent, consistent with previous qualitative findings [13]. Additionally, timeline cyclical items (original IPQ-R sub-scale, describing the extent to which respondents perceive the illness as fluctuating over time) loaded together with the ‘reactive’ items. This was not entirely unexpected as we had previously theorised that these dimensions may overlap [13]. We propose that the new sub-scale now more fully captures the extent to which people see OCD as changing and reacting to internal (e.g. mood) and environmental influences (e.g. life pressures).

The final dimension from the set of main-scales was formed through the combination of the personal control and treatment control sub-scales, creating a general ‘control’ sub-scale. Though Moss-Morris et al. [4] retained both these sub-scales separately in the IPQ-R, they nevertheless noted cross-loading between the two and emphasised that the importance of their distinction may vary depending on the condition assessed. Our previous qualitative study suggested that participants’ sense of greater personal control resulted from skills learned through psychological therapies, such as abstaining from performing rituals [13]. Perhaps in the case of our sample, the majority of whom had received previous cognitive-behavioural therapy (CBT) for OCD, these constructs are too inter-dependent to be distinguishable. This raises a broader point about whether these two control aspects are more closely aligned in mental health (as opposed to physical health) due to the reliance in therapies such as CBT, on behavioural changes made by the individual [30].

The cause scale largely consists of items generated through the qualitative interviews and thus closely reflects the perceptions of people with OCD. Factor analysis of the resulting scale led to the identification of four sub-scales, representing environmental stress, biological causes, learned behaviour and own characteristics or behaviour.

The main sub-scales were found to be internally consistent, with the exception of the spectrum sub-scale (α .592), which only had three items; fewer items are known to be associated with lower α values [23]. Two of the cause sub-scales also fell below the .7 criterion. It has been suggested that, when developing new scales, an alpha of .5 is sufficient to warrant further scale development [26]. As this was the first attempt to measure these constructs (spectrum, biological causes and own characteristic causes) in OCD, these values could be argued to be acceptable, however future iterations should seek to improve them.

Due to the unavailability of criteria for interpreting τ correlations, we used equivalent criterion values for small, medium and large correlations, as well as the minimum test-re-test value, using a table for converting r to τ. All sub-scales exceeded the minimum equivalent value of r > .7 (τ > .49) for test re-test reliability, suggesting that the IPQ-O is reliable. Although within acceptable limits when using Kendall’s τau, the weaker performance of the spectrum sub-scale scale may again be due to the low number of items in this sub-scale. With so few items, small changes in item scores over time would have made a greater relative difference to total score values compared to sub-scales with a larger number of items. Additional items could be added to the spectrum scale in a future iteration of the measure to strengthen this sub-scale’s test-re-test reliability, alongside its internal consistency.

The pattern of correlations between IPQ-O sub-scales and other scales which were expected to be theoretically linked, generally supported the validity of the IPQ-O sub-scales. For example, a stronger illness identity, believing OCD to be permanent, having many negative consequences and a strong emotional representation, were associated with higher levels of depression and anxiety. Conversely, perceptions of having control over OCD was associated with better functioning and lower depression.

As the CSM suggests that perceptions of illness should drive behaviours to deal with the illness, including help-seeking behaviours, we were interested to see whether previous therapies received and intention to seek further therapy were associated with the IPQ-O illness perception dimensions. Those who had received talking therapy perceived greater control over their OCD than those who had not. Since learning skills to self-manage problems is a key goal of talking therapies such as CBT [31], this finding makes conceptual sense, and is in line with the CSM which holds that the results of actions (such as therapy seeking) are appraised, and the results of that appraisal fed back into the model, potentially modifying it [1]. People who received medication for OCD had lower scores on the spectrum sub-scale. It seems plausible that people who perceive OCD as a ‘trait’ present to differing extents throughout the population (as opposed to an illness) would reject a ‘medicalised’ view of OCD as an ‘illness’ and be less willing to take medication as a result. This is consistent with findings of an OCD treatment preference study, which showed that some people do not view medication as appropriate treatment for ‘psychological’ problems [32]. Though inferences about cause and effect cannot be derived from this analysis, further longitudinal research which tests this premise is warranted, as if linked in the posited way, such beliefs could influence the uptake of potentially efficacious treatments such as selective serotonin reuptake inhibitors (SSRIs) [33]. Although differences between perceptions of OCD permanence between those who had and had not taken medication for OCD were not significant, findings were close to significance, with a higher level of perceived permanence in those who had received medication.

We could not assess whether there was a relationship between those who had received no previous treatment versus having received any treatment and IPQ-O sub-scales, as so few individuals had received no previous OCD treatment. This suggests that our sample may be biased towards individuals who seek help and engage in treatment. Our recruitment methods, which relied heavily on advertising via OCD charities mean that we are likely to have recruited individuals who were already engaging in help seeking and therefore, were more likely to have received treatment. Though there is a known gap between symptom onset and treatment [10], recruiting treatment naïve individuals who have a diagnosis of OCD is likely to be difficult as diagnosis is likely to be given at the point of treatment access.

As expected, people who planned to seek NHS treatment (e.g. GP, IAPT services) saw OCD as more permanent. This prediction was based on previous findings that expectations of a long timeline in other conditions were associated with treatment use [34]. However, an alternative prediction could have been made based on the ‘new’ meaning of our sub-scale, that perceptions of OCD as permanent part of the self might lead to individuals to perceive treatment as futile and therefore not worth seeking. Our qualitative findings, however, showed that despite participants having received psychological therapy for OCD, most nevertheless saw the condition as permanent [13]. Although many thought treatments had improved or could improve their condition, most remained doubtful that treatment could ‘cure’ their OCD. This suggests that individuals may still be willing to seek treatment despite doubts about its curability. A better question may therefore not be whether individuals plan to seek therapy, but whether perceptions of permanence impact on outcomes of psychological therapy, as pessimism could impede progress made during treatment e.g. engagement in exposure exercises. Future studies could investigate this by administering the IPQ-O at the start of treatment and examining whether perceptions predict outcome.

Spectrum beliefs were negatively associated with OCD severity, functional impairment, depression and anxiety severity. This suggests that people who have less severe problems are more likely to see OCD as a trait in the general population. It could reflect a possibility that people who ‘normalise’ OCD as something everyone has to differing extents, are less distressed.

Recruitment of a large sample has made it possible to employ factor analysis to derive a modified OCD-specific questionnaire, capable of capturing the way people understand the condition. Development of the IPQ-O using qualitative data has led to the identification of types of illness perception not previously assessed in other conditions. Of particular significance, the spectrum scale could be considered an ‘anti-illness’ dimension of the IPQ-O, which measures perceptions of the condition as a ‘trait’. The measure demonstrates internal consistency, test-re-test reliability and convergent validity. Future studies should test the identified factor structure of the measure using a new sample, through confirmatory factor analysis [24].

The current study has demonstrated that perceptions of OCD are associated with important aspects of adjustment and treatment behaviours (use of talking therapies and medication). Though help-seeking plans were less reliably associated, this was possibly due to the majority having already engaged in treatment, including talking therapies. Longitudinal studies are now needed to test whether the identified perceptions drive outcomes; for example, by examining whether baseline illness perceptions drive outcomes after treatment. If illness perceptions drive behaviours and adjustment to OCD as hypothesised by the CSM, this would indicate a need to address perceptions that negatively affect coping behaviours and adjustment as part of future interventions. For example, if perceptions of OCD on a spectrum hinder use of medication for OCD, health professionals might seek to challenge this perception as part of individual therapy, as well as through future initiatives (e.g. in primary care) that promote help seeking and treatment use in OCD. The IPQ-O offers a reliable and valid tool to assess perceptions of OCD in clinical and research settings alike.