Constipation is a common problem in children worldwide, with an estimated prevalence of up to 30% and similar rates reported for boys and girls (1). Functional constipation (FC) is defined as constipation without a known organic cause, and is characterized according to the Rome III criteria as the presence of 2 or more of the following: 2 or fewer defecations per week, painful defecation, history of retentive posturing, presence of a large fecal mass in the rectum, and passage of hard or large stools (2). In up to 84% of patients, chronic constipation results in episodes of fecal incontinence (FI) (3).
FC in children and adolescents can result in abdominal pain, poor appetite, bloating, and increased absences from school (4–6). In addition, children with FC and FI report more psychological and behavioral problems, such as depression, anger, and low self-esteem, than healthy children (7–9). FC and FI also affect social relations, resulting in lower health-related quality of life (HRQoL) (10,11).
HRQoL is an increasingly important outcome measure in pediatric health care and clinical trials (12–14). HRQoL data can be used to help evaluate how different treatment options affect health outcomes (15). HRQoL is regarded as a multidimensional construct incorporating at least 3 broad domains: physical, mental, and social functioning (16,17). These domains should be assessed from the patient's perspective whenever possible (18). In HRQoL assessments of children, a combination of child self-report and proxy report by a parent or caregiver is preferred because this allows multiple perspectives to be obtained (19), especially for children who are too young to complete patient-reported outcome instruments independently (20). Only 3 studies of HRQoL in children with FC have measured the broad domains of HRQoL (6,21,22), 2 of which used both child self-report and parent proxy report for younger children (6,22), and none of which included children ages 2 to 4 years.
The Pediatric Quality of Life Inventory version 4.0 Generic Core Scales (PedsQL) (23) is the only pediatric HRQoL instrument that can be used across a wide age range (2–18 years) and that measures the 3 broad domains of HRQoL as well as school functioning. The PedsQL, which includes both self-report and proxy report for individuals ages 5 to 18 years, has been translated into >70 languages and has been widely used with children, being reported in approximately 500 peer-reviewed journal publications to date. The PedsQL has demonstrated good validity in healthy children (24) and in a number of specific pediatric populations, such as individuals with cancer (25), rheumatic disease (14), heart disease (26), type 1 or type 2 diabetes mellitus (27), and asthma (28).
The present study evaluates the psychometric properties of the Dutch translation of the PedsQL in children with FC ages 2 to 18 years in the Netherlands.
This multicenter study enrolled patients ages 2 to 18 years who attended a pediatric outpatient clinic in a secondary or tertiary care center from 2010 to 2013 and met the Rome III criteria for FC (2). Children with organic causes of constipation were excluded.
The parent proxy reported version of the PedsQL and the PedsQL Gastrointestinal Symptoms Module (GI module) were distributed to the parents of all of the children and adolescents who met the above criteria, and the child self-reported version was given to patients ages 5 to 18 years. Children and parents could complete the questionnaire at the clinic or at home. Patients ages 8 to 18 years were informed in an attached letter that they were to complete the questionnaires by themselves without discussing answers with their parents. Parents and research assistants administered the questionnaires to children ages 5 to 7 years using an interview format. They were explicitly instructed not to help the children answer the questions, but only to read the questions out loud. The total time required to complete the questionnaires was approximately 15 to 20 minutes per person (parent or child).
All of the parents and children ages 12 to 18 years gave informed consent. Children <12 years of age were assumed to be too young to give informed consent. The study was approved by the medical ethical committee of the St Elisabeth Hospital, Tilburg, the Netherlands, which represented all of the centers involved in the study.
The Amsterdam Medical Center questionnaire (29) was used to collect data on clinical characteristics regarding the presence of FC. Items were rated on a 3-point scale and dichotomized so that “yes” and “sometimes” indicated the presence of a complaint and “no” its absence. For the purpose of the present analyses, form of defecation was re-coded as hard = 1, normal = 0, soft = 0, and liquid = 0. A higher score indicated more symptoms.
The PedsQL (23) comprises 23 items assessing 4 domains of HRQoL: physical functioning (8 items), emotional functioning (5 items), social functioning (5 items), and school functioning (5 items). To generate a psychosocial health summary score, the sum of the recorded scores for the emotional, social, and school functioning scales is divided by the number of items answered in these scales.
The PedsQL has previously been translated and validated in Dutch (24,30). The PedsQL takes approximately 5 minutes to complete. The PedsQL for children ages 2 to 4 years is in proxy format only, whereas for those ages 5 to 18 years it is both self-reported and proxy reported. The PedsQL self-report for children ages 5 to 7 years is interview administered.
Response options for all items on the parent proxy report form and the child self-report form for patients ages 8 to 18 years are graded on a 5-point scale (0 = never, 1 = almost never, 2 = sometimes, 3 = often, and 4 = always). The self-report form for children ages 5 to 7 years uses a 3-point scale (0 = not at all a problem, 2 = sometimes a problem, and 4 = a lot of a problem), with each response choice anchored to a happy, neutral, or sad face. In all cases, a 1-month recall period is used. Item responses are reverse scored and linearly transformed to a 0 to 100 scale (0 = 100, 1 = 75, 2 = 50, 3 = 25, and 4 = 0), with a higher score indicating a better HRQoL (23). Domain scores were computed as the sum of the item scores divided by the number of items answered. If >50% of the items in the domain were missing, the scale score was not computed (14).
The PedsQL GI module is a disease-specific extension to the overall PedsQL (31) and was completed by all of the parents and children ages 5 to 18 years. The GI module also has a 1-month recall period. It consists of 1 scale with 9 symptoms (pain in stomach, diarrhea, constipation, nausea, vomiting, discomfort in stomach, passing gas, not feeling hungry, and bloating); the severity of each is scored on a 5-point scale that uses the same responses as the PedsQL. The GI module is scored in the same way as the PedsQL, including transformation of the score to a 0 to 100 scale. Higher scores indicate fewer symptoms and better functioning.
Defecation Disorder List
The defecation disorder list (DDL) was also completed by children ages 8 to 18 years. The DDL is a disease-specific questionnaire that evaluates the impact of functional defecation disorders (29). It consists of 37 items across 4 domains: constipation, emotional functioning, social functioning, and treatment/interventions. Each item uses a 5-point graded response scale (0 = never or no, 1 = almost never or a little bit, 2 = sometimes or a fair bit, 3 = often or quite a lot, and 4 = almost always or very much) with a 2-week recall period. To compute the scale scores, items are reverse scored and linearly transformed to a 0 to 100 scale (0 = 100, 1 = 75, 2 = 50, 3 = 25, and 4 = 0), with higher scores indicating better disease-specific HRQoL.
A previous study found that good internal consistency reliability could not be replicated for the constipation domain of the DDL (Cronbach α 0.35) and the treatment/interventions domain (Cronbach α 0.53) (21). Therefore, only the DDL emotional functioning and social functioning domains were used in the present study.
The distribution abnormalities of the PedsQL were determined by examining the proportion of missing item-level responses (32). The adequacy of the range of measurement was based on floor effects (lowest possible scores) and ceiling effects (highest possible scores). The scales were considered to be absent of floor or ceiling effects if <15% of the sample scored either the lowest possible score (floor effect) or the highest possible score (ceiling effect) (33). Internal consistency reliability was determined by calculating Cronbach α (34). An α of 0.70 or greater suggests satisfactory internal consistency reliability (35).
Patient–parent agreement was evaluated using paired t tests and intraclass correlation coefficients (ICCs) (36,37). Effect sizes for differences in means between child self-reports and parent proxy reports were designated as small (0.20), medium (0.50), and large (0.80) (38). The ICC is an index of absolute agreement and takes into account the ratio between subject variability and total variability. A 2-way mixed model (absolute agreement, single measure) was used to calculate the ICCs. ICCs were classified as follows: not more than 0.40 = poor to fair agreement, 0.41 to 0.60 = moderate agreement, 0.61 to 0.80 = good agreement, and 0.81 to 1.00 = excellent agreement (36).
Construct validity was assessed by correlating the PedsQL with the GI module and the DDL. It was hypothesized, a priori, which domains of the PedsQL would correlate with domains assessed by the GI module and the DDL. It was predicted that more severe symptoms as assessed with the GI module would be associated with greater impairment of PedsQL scores. Relations between the PedsQL and the GI module were examined with Pearson product moment correlations, designated as small (0.10), medium (0.30), and large (≥0.50) (38). It was predicted, a priori, that the PedsQL psychosocial scale would correlate more highly than the PedsQL physical scale with the DDL emotional and social functioning scales. Inferences regarding convergent and divergent validity were based on the patterns of correlations among the measures. Although convergent validity correlations were generally expected to be moderate (0.30 < r ≤ 0.50) or large (r > 0.50), divergent validity correlations were expected to be relatively weak (r ≤ 0.30).
A preliminary evaluation of the discriminating ability of the PedsQL was conducted by computing single sample t tests comparing the mean scores of the present sample with published means of healthy US children (14). On the basis of previous findings (6), it was anticipated that healthy children would report higher PedsQL scores than children with FC. Effect sizes were calculated to determine the magnitude of this difference and were designated as small (0.20), medium (0.50), and large (0.80) (38). In addition, analyses of variance were used in the present sample of children with FC to test for mean differences in PedsQL scores between patients classified into known groups based on responses to items from the GI module and the DDL. It was hypothesized that patients who answered 0 (never) or 1 (almost never) on the bloating, pain, passing gas, discomfort, and constipation items of the PedsQL GI module, as well as the DDL item “I worry sometimes that I can’t do a poo,” would have better PedsQL scores than patients who responded with 3 (often) or 4 (almost always).
Sociodemographic and Disease Characteristics
In total, 269 children with FC were enrolled in the study. The mean age of the children was 7.8 years (standard deviation [SD] 4.1); 58% were girls (Table 1). Almost all of the children were Dutch (98%); the remainder were Dutch speaking. Overall, 83% of children had experienced symptoms of constipation for >6 months and 85% were taking medication for their constipation. When the Rome III criteria were examined individually, 25% of children had a defecation frequency of <3 times per week, 58% had FI at least once per week, 63% had a history of withholding behavior, 60% had painful defecation or hard stools, 60% had a history of passing large stools, and 86% had a large fecal mass in their abdomen when examined at enrollment.
Overall, 5.3% of patient self-reports and 2.6% of parent proxy reports had >50% of their item responses missing (Table 2). The proportion of individuals who failed to respond to >50% of the items varied from 2.3% (5–7 years) to 9.5% (8–12 years) for patient self-reports and from 0% (5–7 years) to 6.7% (2–4 years) for parent proxy reports.
Although there was no evidence of floor effects, ceiling effects were observed for social functioning in all age groups for both patient self-report and parent proxy report (Table 2). Ceiling effects were also observed for physical health (overall parent proxy report, ages 5–7 years parent proxy report, and age 13–18 years patient self-report) and school functioning (overall parent proxy report, age 2–4 years parent proxy report, and age 5–7 years patient self-report).
Internal Consistency Reliability
Cronbach α was 0.70 or greater for the overall scores and for the majority of subscales (Table 2), indicating satisfactory internal consistency. The exceptions were self-reported physical health and emotional functioning in children ages 5 to 7 years, as well as self-reported school functioning in all age groups and parent proxy reported school functioning in all age groups other than children ages 2 to 4 years.
Mean PedsQL scores are shown in Table 3. In the overall patient population, statistically significant differences (P < 0.05) between patient self-report and parent proxy report were seen in the psychosocial health and emotional functioning domains, with children reporting better functioning than their parents.
When the age groups were examined individually, statistically significant differences (all P < 0.05) in the social functioning domain were observed across all age groups; however, these differences were not consistent in their direction across groups. In children ages 5 to 7 years, parents reported better social functioning than did children, but in the older age groups (8–12 and 13–18 years), this trend was reversed, with children reporting significantly higher social functioning scores than parent proxies. In the 2 older age groups, the mean total PedsQL score was also significantly higher for patient self-report than for parent proxy report. This trend was seen in the majority of the subscales.
The ICCs demonstrated moderate patient–parent agreement for the overall patient sample (Table 3) and good agreement for children ages 8 to 12 years and adolescents (13–18 years). ICCs were lowest in the youngest age group (5–7 years), ranging from 0.29 for physical health to 0.53 for social functioning.
Correlations between the PedsQL scales and the GI module were positive in direction and statistically significant for both patient self-report and parent proxy report in >80% of the hypothesized relations (Table 4). There was, however, no overarching pattern to the correlations. The correlations between GI module scores and parent proxy reported PedsQL psychosocial health scores (r = 0.27), including emotional functioning (r = 0.29) and social functioning (r = −0.02), were not statistically significant in children ages 5 to 7 years.
Convergent and divergent validity results were mixed. In many cases, the correlations showed the expected pattern; for example, patient self-reported DDL emotional functioning and social functioning scores correlated more highly with the PedsQL psychosocial health scores (r = 0.33–0.68) than with the PedsQL physical health scores (r = 0.02–0.67). This pattern of correlation was, however, not evident with parent proxy reported scores, with DDL emotional functioning and social functioning correlating to a similar extent with PedsQL psychosocial health (r = 0.27–0.38) and physical health (r = 0.05–0.57).
The comparisons between the means of the overall population of Dutch children with FC (ages 2–18 years) and those of a healthy US reference sample of the same age range (14) showed that children with FC scored lower than healthy children on all PedsQL subscale scores. This was true for patient self-report and parent proxy report. Effect sizes ranged from small to large and were smaller for the comparisons of patient self-reports (0.26 ≤ d ≤ 0.53) than for parent proxy reports (0.47 ≤ d ≤ 0.85).
Children were classified into subgroups based on the severity of their symptoms using the GI module and the DDL. The known-groups analyses of variance provided satisfactory support for the discriminating ability of the self- and proxy reported PedsQL total, physical health, and psychosocial health scores. For all comparisons evaluated, patients who answered 0 (never) or 1 (almost never) for a symptom had better PedsQL scores than patients who responded with 3 (often) or 4 (almost always). Subgroup differences were, however, not always statistically significant for the PedsQL emotional functioning, social functioning, and school functioning scores, and the PedsQL GI module passing gas item yielded no statistically significant differences across known groups (supplemental table, http://links.lww.com/MPG/A363). Table 5 displays the known-groups results for the constipation item of the PedsQL GI module. It can be seen that patients who answered 0 or 1 on the constipation item (indicating that they had problems with constipation never or almost never during the past month) scored higher on all PedsQL scores compared with patients who answered 3 or 4 (indicating problems often or almost always during the past month); all differences were statistically significant apart from the difference in social functioning scores (Table 5).
The primary objective of this study was to evaluate the psychometric properties of the Dutch translation of the PedsQL 4.0 Generic Core Scales (23) in children with FC in the Netherlands. Overall, the instrument showed acceptable initial psychometric properties for children and adolescents ages 8 to 18 years; however, further research is needed into the reliability and validity of the PedsQL subscale scores among children ages 5 to 7 years.
In the present study, the majority of the PedsQL scales displayed no ceiling effects, with the exception of the physical health and social functioning scales in the overall sample for both self- and proxy reports. In general, these ceiling effects may be expected given that the items involve normal activities and the children in the sample were relatively healthy. Examples of the items of the physical health scale are “it is hard for me to walk more than 1 block” (item 1), “it is hard for me to run” (item 2), and “it is hard for me to do sports activity or exercise” (item 3)—healthy children will not generally complain about walking, running, or playing. Although it may be possible to identify reasons for these ceiling effects, the fact remains that their existence can make movement on the PedsQL physical health and social functioning scales difficult to observe—both between subjects (low sensitivity) and within subjects (low responsiveness). Therefore, these 2 scales may be incapable of showing improvement owing to treatment, which is cause for concern. It should, however, be noted that the large number of children scoring at the high end of the PedsQL social functioning scale does not preclude defecation-related social problems resulting from FI, which was found in previous research using constipation-specific questionnaires (21). A high ceiling effect was also seen in the school functioning domain for children ages 2 to 4 years, which indicated that 48.2% of children ages 2 to 4 years achieved a perfect school functioning score of 100. We recommend that the content validity of the PedsQL school functioning items for children ages 2 to 4 years, and the instructions for parent proxy reporting, should be separately appraised with qualitative research involving parents of young children with FC.
Internal consistency reliability met the conventional standard of 0.70 or greater for group comparisons for all PedsQL scales except for self-reports of children ages 5 to 7 years and the school functioning subscale in most age groups for both self- and proxy report. The finding of low internal consistency in children ages 5 to 7 years is consistent with a previous study of the Dutch translation of the PedsQL in children with psychiatric disorders (24,30), which reported low internal consistency reliability (α < 0.60) for all PedsQL self-reported subscales in children ages 6 to 7 years; however, large-scale studies showed the PedsQL self-report to be reliable in both healthy and chronically ill US children ages 5 to 7 years (14,39). This could reflect differences in methodology. In the US studies (14,39), most self-reports were assessed by mail with instructions for parents to interview and assist their children with completion of the questionnaire. In the Dutch study (30), however, children completed the self-reports separately from their parents, with the help of a research assistant (information provided by the authors). Most children in the present study completed the self-report version separately from their parents, with assistance from research assistants if needed. It has been demonstrated that different completion methods and help from parents can explain differences in children's capability to self-report their HRQoL reliably (40). Because the internal consistency of the subscales varies across age groups, and is unsatisfactorily low in children ages 5 to 7 years, inferences based on the subscale scores are problematic.
Similarly to other studies that assessed the level of agreement between self- and proxy reports (41,42), the present study found moderate to large ICCs, which generally indicated satisfactory interrater reliability for children ages 8 to 12 years and adolescents (13–18 years). In both of these age groups, patient self-reported HRQoL was higher than parent proxy reported HRQoL. Earlier studies also showed a similar parental tendency to underestimate the HRQoL of their sick children (43–46); however, in the sample of children ages 5 to 7 years, parent proxy reports indicated a better HRQoL than children's self-reports. Although we have no explanation for this unusual pattern, these anomalous results, together with the low internal consistency in this age group, call into question the utility of PedsQL scales for Dutch children with FC ages 5 to 7 years.
Construct validity was examined by testing correlations between the PedsQL and the GI module. All hypothesized correlations were statistically significant in the self-reported PedsQL scores in the total group; in the analyses of the separate age groups, the associations were predominantly in the predicted direction and were statistically significant, which is a positive indication for the construct validity of the PedsQL in children with FC; however, the empirical results regarding convergent and divergent validity were mixed. In many cases the correlations showed the expected pattern: self-reported DDL emotional functioning and social functioning scores correlated more highly with the PedsQL psychosocial health scores than with PedsQL physical health scores in the overall sample. In contrast, the predicted pattern of correlations was not evident for parent proxy reports.
Consistent with the results of earlier studies (47,48), the PedsQL appeared to discriminate between healthy children and those with a chronic illness. In the present analyses, children with FC reported lower HRQoL than healthy US children on all of the subscales, with medium-to-large effects for both self- and proxy reports, thereby supporting their discriminating ability. The data on healthy children were, however, derived from previously published literature rather than from children recruited in the present study. Therefore, known-groups comparisons were conducted between subgroups of patients with different symptom severities. These analyses showed that the PedsQL is capable of discriminating between children with mild and severe symptoms on the physical and psychosocial health summary scales, including bloating, pain, discomfort, and constipation; notably, this was in the presence of pronounced ceiling effects, confirming the discriminating ability of the PedsQL.
A number of limitations of this study should be acknowledged. First, given the cross-sectional design of the study, test–retest reliability and responsiveness to change could not be assessed. Although studies of other pediatric groups have shown satisfactory test–retest reliability with the PedsQL (49), these missing evaluations are a limitation of the present study. Second, content validity was assumed but not confirmed with additional qualitative research. Third, it was not possible to compare these data with data from healthy Dutch children, because enrolling a separate control cohort was outside the scope of the present study and there are no published data from the Netherlands that could be used as a comparison group for both child self-report and parent proxy report across the whole age range used in the present study (24,30). These data are only available in the original PedsQL validation study, which was performed in healthy children in the United States (14). Hence, these data were used as a comparison for assessment of discriminating ability.
In conclusion, the results of this study showed satisfactory measurement properties of the Dutch translation of the PedsQL generic core scales, both child self-reported and parent proxy reported, in children ages 8 to 12 years and adolescents (13–18 years) with FC. Specifically, the total, physical health, psychosocial health, emotional functioning, and social functioning scores may be useful scales for assessing HRQoL in Dutch children ages 8 to 18 years who have FC. The school functioning subscale is, however, not recommended for use in Dutch children with FC in any age group. In addition, the self-report version of the PedsQL is not recommended for use in children ages 5 to 7 years with FC, and additional research is required to examine the construct validity and internal consistency of the PedsQL in this age group. Further research is also needed into the content validity of the PedsQL for children ages 2 to 4 years, and the overall test–retest reliability of the PedsQL and its responsiveness to change. HRQoL in pediatric patients with constipation is an important issue, and there is limited information available in the literature. The findings of this study are therefore relevant for clinicians and investigators working with pediatric patients with constipation and will help them to better understand their patients’ HRQoL and inform future research in this area.
The authors thank Catherine Hill, PhD, an employee of PharmaGenesis London, who was funded by Shire to provide editorial support for this publication.
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