Psychometric properties of the questionnaire on threat perception of chronic illnesses in pediatric patients*

Objective: the objective of the study was to assess the psychometric properties of the Brief Illness Perception Questionnaire in a sample of adolescents with chronic endocrine or pneumological conditions and to analyze the dimensionality and reduce the scale elaborating scales by sex and medical diagnosis. Method: we evaluated 510 patients aged 9-16 years using the Brief Illness Perception Questionnaire and the Hospital Anxiety and Depression Scale. We carried out tests of reliability, construct and criterion validity and a comparison of means based on the diagnosis and socio-demographic variables. The reliability and validity analyses showed adequate psychometric properties for this scale, with better results obtained for a single dimension after eliminating 3 items. Results: adolescents with type 1 diabetes and girls were found to have an increased threat perception of their illness. Anxiety/depression was positively associated with the perception of illness. Conclusion: this questionnaire is a useful and practical tool for evaluating adjustment to illness in pediatric patients.


Introduction
The evaluation of the perception of illness has aroused great interest (1) as it may affect patients' quality of life, well-being and adherence to treatment, among other factors (1)(2)(3)(4)(5)(6) . Those who perceive their illness as more threatening, appear to present more anxiety, depression and a poorer quality of life (1)(2)(3) .
The processing of emotional and cognitive responses to illness helps patients to regulate themselves emotionally in order to better adapt to their condition, which can in turn change their cognitive or emotional representation. The term "perception of illness" therefore refers to a patient's mental representations of their illness, in relation to its identity (name and symptoms), causes, consequences, course and control (7)(8) .
All this seems particularly relevant in the case of chronic diseases (CD), since these are health problems that persist over time and requires continuous management and lifestyle changes over the years, and may affect the possible future evolution of the disease (9) .
However, not all CD appear to have the same effects. These effects seem to be more serious in the case of endocrine diseases, such as Diabetes Mellitus Type 1(DM1), than in respiratory diseases, such as asthma (10) .
Despite its importance, few studies have addressed this concept in adolescence, a particularly complicated period with lower rates of adherence to treatment, a greater presence of risk behaviors and more psychopathological problems (5,11) .
Although there are different models and instruments for the study of adaptive response to disease (12)(13) , the prevailing model in the literature for some years has been the Common Sense Self-Regulation Model (14) . Based on this model, the Illness Perception Questionnaire (IPQ) (10) was designed, and is probably the most widely used instrument at international level for assessing this construct (1,15) . It initially had 38 items, and an extended revised version (IPQ-R) was subsequently designed, consisting of 70 items, including cognitive and emotional responses (16) . In recent years, in order to simplify and facilitate its application, the short IPQ (IPQ-R) was developed. This is composed of 9 items (10) providing a quick and simple evaluation of this construct (17) .
The IPQ-R has been used in 36 countries and translated into 26 languages, and has been used in numerous diseases (2)(3)(18)(19) among patients aged 8 to 80 years old. The linguistic adaptation of IPQ-R to Spanish was carried out with adults with different CD, including endocrines and respiratory (15) . However, despite its widespread use, few studies analyze its psychometric properties (2,(20)(21)(22) , and these are even more scarce in the Spanish context (15) . Likewise, there do not appear to be any studies analyzing the psychometric properties of IPQ-R pediatric patients with chronic conditions. One aspect in relation to this instrument that continues to be a source of debate refers to its dimensionality. While some studies suggest using each item as a subscale (17) , others postulate the existence of two (cognition and emotion) (18) or three dimensions (adding understanding of the disease to the two previous dimensions) (20) . Similarly, there seems to be no consensus on the effect that sex, age, or type of disease have on threat perception (10,(23)(24) .
Another limitation of the instrument refers to the non-existence of interpretative scales that facilitate its interpretation depending on the type of disease or chronic condition.
The main objective of the study will therefore be to analyze the psychometric properties of BIP-Q in a sample of chronically ill adolescents, while studying the dimensionality of the scale and the effect of age, sex and medical diagnosis, and to offer interpretative scales.
This will all enable the development of intervention and prevention programmes that improve the quality of life of these patients.

Method
The participants (n=510) were adolescents with chronic diseases between 9 and 16 years of age  Questionnaire (IPQ-R) and the Hospital Anxiety and Depression Scale (HADS).

The Spanish version of the Brief Illness Perception
Questionnaire (IPQ:R) (10,15) consists of 9 items. The first 8 items (consequences, duration, personal control, treatment control, identity, concern, emotional response and understanding of the disease) are answered on a and the type of sample (2,10,15,(20)(21)(22) .

The version of the Hospital Anxiety and Depression
Scale (HADS) (25) adapted to Spanish (26)  For data analysis: first, the reliability of the scale (Cronbach alpha, composite reliability (CF) and mean extracted variance index (MEVI)) was analyzed, and its validity (exploratory factorial analysis (EFA), confirmatory factorial analysis (CFA) and predictive validity of the instrument) was then analyzed. The EFA was performed using the recommended process (29) using the unweighted least squares (ULS) method, parallel analysis and direct Oblimin rotation. The CFA were carried out by means of robust estimation of maximum likelihood (ML), with the objective of correcting the absence of multivariate normality. The suitability of the CFA was tested using the chi-square significance and robust Satorra-Bentler adjustments (S-B χ²) (30)(31) , the ratio between χ² and its degrees of freedom (χ²/df), as well as the S-B X² and its degrees of freedom (proper setting≤5) (32) , the comparative setting index (CFI), the incremental setting (IFI) (proper setting≥.90) (33) and the mean square error approach (RMSEA) (proper setting≤.08) (34) .
The relationship between BIP-Q and HADS was then analyzed using multiple hierarchical linear regressions, followed by differences in means according to the diagnosis (single factor ANOVA), sex and the two age groups of preadolescents (9-12 years) and adolescents (12-16 years) (t-test). They were recoded into two groups by age. Finally, scales were calculated based on centile scores according to diagnosis and sex. Statistical analyses were performed using SPSSv24, FACTOR (35) software and EQSv6.3.

Results
The participants (n=510) were minors with chronic diseases between 9 and 16 years old (M=12.03, SD=2.05), 42.4% (n=216) were preadolescents (9-12 years old) and 55.6% (n=294) were adolescents (12-16 years old). 54.5% of them were children (n=278).  and 7) ( Table 2). After these re-specifications, both models presented a suitable fit although the fit indices  Finally, in order to facilitate the interpretation of the scores, the main centiles were calculated according to diagnosis and sex, ignoring age groups, given the lack of differences between these groups (Table 3).

Discussion
The presence of CD in adolescence, whether endocrinological or pneumological, may be perceived as a threat to health and survival (11) , which may influence the course and resolution of the disease (6,8) . It is therefore necessary to have instruments for its measurement (12)(13) , and the BIP-Q is the most widely used (2,17,20), However, to date, psychometric properties have not been analysed in adolescents with CD, or in the specific case of Spain. Our study therefore aims to analyze the psychometric properties of BIP-Q in a sample of 510 adolescents with CD.
After analysing the psychometric properties, the final number of items was reduced to 5, thereby obtaining the reduced version presented in this study that presents adequate psychometric properties.
Although the scale itself was already reduced, it was necessary to eliminate items because when analyzing the psychometric properties in our study sample, the adjustment indices were not adequate, and as such the reliability and validity of the questionnaire improved significantly after items 3, 4 and 7 were eliminated. As regards the dimensionality of the scale (1,17,20) , although both the unifactorial and the bifactorial models seem adequate, and the unifactorial model generally seems As for criteria validity, as suggested by the literature (1)(2)(3) , the main predictor of anxiety-depressive symptomatology is the level of perception of illness threat, followed by age.
Regarding the analysis of the influence of sociodemographic variables with respect to the perception of illness threat, as suggested by previous research (10) , there are differences depending on the type of disease, as adolescents with DM1 show higher levels of threat than adolescents with respiratory problems.
Likewise, there are no differences according to age, as indicated in the literature (36) , but there are differences according to sex, as in the specialized literature (24) .
Finally, in order to facilitate diagnosis, interpretation scales are presented that can help health professionals to assess the threat perception of their CD patients quickly and easily. context has only been used in adult populations (15) but not in adolescent populations. The fact that the questionnaire is not specific to a chronic disease as such, but that it allows substitution of terms such as asthma or diabetes, medical treatment by inhalers or insulin when it is completed facilitates its use. It is therefore useful for any pediatric CD, as well as being easy to administer and correct. The BIP-Q questionnaire is therefore a useful and practical tool with which to evaluate the adjustment to disease.

Conclusion
The results of this study show that the reduced Spanish version of the Disease Perception Questionnaire (BIP-Q) is a reliable, valid instrument with solid psychometric properties, which works effectively in the evaluation of the threat perception of pediatric chronic diseases