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Statistical considerations for use of composite health-related quality-of-life scores in randomized trials.

ABSTRACT: Quality of life instruments are frequently used as outcomes in randomized trials. Instruments that consist of several subscales present researchers with a choice of whether to combine some or all scales into a single composite score. There may be several clinically and scientifically reasonable alternative combinations of subscales for the primary outcome measure.The statistical efficiency of different combinations of subscales depends on the relative effect size of the intervention on each subscale and the correlation between the subscales. Simple equations can be derived for determining the relative statistical efficiency of each clinically reasonable combination of subscales. Hypothetical scenarios show that the number of patients needed in a clinical trial can be twice as great for some combinations of subscales as for others.There are often compelling clinical or scientific reasons to use a particular subscale or composite in a randomized trial. In the case where a number of different alternatives would be reasonable, statistical efficiency can help guide the choice of endpoint.

SUBMITTER: Vickers AJ

PROVIDER: S-EPMC2613680 | biostudies-literature | 2004 May

REPOSITORIES: biostudies-literature

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Statistical considerations for use of composite health-related quality-of-life scores in randomized trials.

Vickers Andrew J AJ

Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation 20040501 4

<h4>Background</h4>Quality of life instruments are frequently used as outcomes in randomized trials. Instruments that consist of several subscales present researchers with a choice of whether to combine some or all scales into a single composite score. There may be several clinically and scientifically reasonable alternative combinations of subscales for the primary outcome measure.<h4>Major findings</h4>The statistical efficiency of different combinations of subscales depends on the relative ef ...[more]

PMID: 15129882

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Project description:Objectives(i) Quantify the relative association between child dental caries experience and maternal-reported child oral health-related quality of life (OHRQoL); (ii) examine whether that association differed according to family socioeconomic status (SES); and (iii) explore whether absolute OHRQoL varied by family SES at similar levels of child caries experience.MethodsThis study was a cross-sectional analysis of children in southern Brazil (n=456, mean age: 38 months) participating in an existing health centre-based intervention study. OHRQoL impact was quantified as mean score on the Brazilian Early Childhood Oral Health Impact Scale (ECOHIS) and compared over categories of caries experience (dmft: 0, dmft: 1-4, dmft: ≥5). Adjusted ECOHIS ratios between caries categories were calculated using regression modelling, overall and within socioeconomic strata defined by maternal education, social class and household income.ResultsCaries prevalence (dmft >0) was 39.7%, mean ECOHIS score was 2.0 (SD: 3.5), and 44.3% of mothers reported OHRQoL impact (ECOHIS score >0). Increasing child caries experience was associated with worsening child and family quality of life: ECOHIS scores were 3.0 times greater (95% CI: 2.0, 4.4) for children with dmft ≥5 vs dmft=0, a pattern that persisted regardless of family socioeconomic status (P for interaction: all >0.3). However, adjusted for dental status and sociodemographic characteristics, mean ECOHIS scores were lower when reported by mothers of less educational attainment (ratio: 0.7; 95% CI: 0.5, 1.0), lower social class (ratio: 0.7; 95% CI: 0.5, 1.0) or in lower income households (ratio: 0.8; 95% CI: 0.6, 1.3).ConclusionDental caries was associated with negative child and family experiences and lower OHRQoL across all social groups; yet, families facing greater disadvantage may report lesser quality-of-life impact at the same level of disease experience. Thus, subjective quality-of-life measures may differ under varying social contexts, with possible implications for service utilization, evaluating oral health interventions, or quantifying disease morbidity in low-SES groups.

Project description:PurposeThere is a need to determine whether health-related quality-of-life (HRQL) assessments in dementia capture what is important, to form a coherent basis for guiding research and clinical and policy decisions. This study investigated structural validity of HRQL assessments made using the DEMQOL system, with particular interest in studying domains that might be central to HRQL, and the external validity of these HRQL measurements.MethodsHRQL of people with dementia was evaluated by 868 self-reports (DEMQOL) and 909 proxy reports (DEMQOL-Proxy) at a community memory service. Exploratory and confirmatory factor analyses (EFA and CFA) were conducted using bifactor models to investigate domains that might be central to general HRQL. Reliability of the general and specific factors measured by the bifactor models was examined using omega (ω) and omega hierarchical (ω h) coefficients. Multiple-indicators multiple-causes models were used to explore the external validity of these HRQL measurements in terms of their associations with other clinical assessments.ResultsBifactor models showed adequate goodness of fit, supporting HRQL in dementia as a general construct that underlies a diverse range of health indicators. At the same time, additional factors were necessary to explain residual covariation of items within specific health domains identified from the literature. Based on these models, DEMQOL and DEMQOL-Proxy overall total scores showed excellent reliability (ω h > 0.8). After accounting for common variance due to a general factor, subscale scores were less reliable (ω h < 0.7) for informing on individual differences in specific HRQL domains. Depression was more strongly associated with general HRQL based on DEMQOL than on DEMQOL-Proxy (-0.55 vs -0.22). Cognitive impairment had no reliable association with general HRQL based on DEMQOL or DEMQOL-Proxy.ConclusionsThe tenability of a bifactor model of HRQL in dementia suggests that it is possible to retain theoretical focus on the assessment of a general phenomenon, while exploring variation in specific HRQL domains for insights on what may lie at the 'heart' of HRQL for people with dementia. These data suggest that DEMQOL and DEMQOL-Proxy total scores are likely to be accurate measures of individual differences in HRQL, but that subscale scores should not be used. No specific domain was solely responsible for general HRQL at dementia diagnosis. Better HRQL was moderately associated with less depressive symptoms, but this was less apparent based on informant reports. HRQL was not associated with severity of cognitive impairment.

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Statistical considerations for use of composite health-related quality-of-life scores in randomized trials.

Publications

Statistical considerations for use of composite health-related quality-of-life scores in randomized trials.

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