The reporting of cluster analysis was found to be generally unsatisfactory, with many studies failing to provide enough information to allow replication or the evaluation of the quality of the research. Clear guidelines for conducting and reporting cluster analyses in health psychology are needed.

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AIM The aim of this study was to develop a valid classification system to describe eating and drinking ability in people with cerebral palsy (CP), and to test its reliability. INTERPRETATION The EDACS provides a valid and reliable system for classifying eating and drinking performance of people with CP, for use in both clinical and research contexts. METHODPeople with cerebral palsy (CP) are affected by a range of activity limitations, attributed to non-progressive disturbances occurring in the developing fetal or infant brain. 1 The motor disorders of CP are often accompanied by disturbances of sensation, perception, cognition, communication, and behaviour, by epilepsy, and by secondary musculoskeletal problems.1 Impairments can limit the oral skills required for eating, drinking, and swallowing, with consequent risks of respiratory problems linked to direct aspiration of food and fluid into the lungs, 2-4 and inadequate nutrition and hydration. 5,6 Activity limitations also affect the ability to bring food and drink to the mouth. The degree to which a person with CP can control the posture and movement of the trunk and head has a direct impact on the efficient use of the muscle systems which support feeding and breathing. 7,8 The prevalence of eating and drinking difficulties in individuals with CP is unclear.9 Estimates depend on the definitions and tools used, ranging from 27% 10 to 90%. 11Prevalence has been proposed to be related to severity of motor impairment, 12 although eating and drinking problems have also been reported to occur in individuals at Gross Motor Function Classification System (GMFCS) levels I and II. 13,14 There is no agreement in the literature about the definition of the terms mild, moderate, and severe in relation to limitations to eating and drinking ability, or whether focus should be at the level of body functions and structures, activity, and/or participation. A recent systematic review identified the lack of a valid and reliable ordinal scale to classify the eating and drinking abilities of people with CP in both clinical and research contexts. 15The purpose of this study was to develop the Eating and Drinking Ability Classification System (EDACS) for people with CP, and evaluate its validity and reliability, making use of defined quality standards. Content validity is considered positive if there is a clear statement of purpose of the assessment and clear identification of the target population and concepts being measured. Content should be identified with input from the target population as well as experts and investigators. Reliability is considered satisfactory if the intraclass correlation coefficient (ICC; or weighted kappa) is at least 0.7 in a sample size of at least 50 patients. 16The EDACS is analogous and complementary to the GMFCS, 17 the Manual Ability Classification System (MACS) 18 or the Communication Function Classification System (CFCS).19 Thus, the intention is for the EDACS Stage 1: Drafting of the eating and drinking ability classification systemThe initial d...

BackgroundThe 12-item General Health Questionnaire (GHQ-12) is used routinely as a unidimensional measure of psychological morbidity. Many factor-analytic studies have reported that the GHQ-12 has two or three dimensions, threatening its validity. It is possible that these 'dimensions' are the result of the wording of the GHQ-12, namely its division into positively phrased (PP) and negatively phrased (NP) statements about mood states. Such 'method effects' introduce response bias which should be taken into account when deriving and interpreting factors.MethodsGHQ-12 data were obtained from the 2004 cohort of the Health Survey for England (N = 3705). Following exploratory factor analysis (EFA), the goodness of fit indices of one, two and three factor models were compared with those of a unidimensional model specifying response bias on the NP items, using structural equation modelling (SEM). The hypotheses were (1) the variance of the responses would be significantly higher for NP items than for PP items because of response bias, and (2) that the modelling of response bias would provide the best fit for the data.ResultsConsistent with previous reports, EFA suggested a two-factor solution dividing the items into NP and PP items. The variance of responses to the NP items was substantially and significantly higher than for the PP items. The model incorporating response bias was the best fit for the data on all indices (RMSEA = 0.068, 90%CL = 0.064, 0.073). Analysis of the frequency of responses suggests that the response bias derives from the ambiguity of the response options for the absence of negative mood states.ConclusionThe data are consistent with the GHQ-12 being a unidimensional scale with a substantial degree of response bias for the negatively phrased items. Studies that report the GHQ-12 as multidimensional without taking this response bias into account risk interpreting the artefactual factor structure as denoting 'real' constructs, committing the methodological error of reification. Although the GHQ-12 seems unidimensional as intended, the presence of such a large response bias should be taken into account in the analysis of GHQ-12 data.