Questionnaire discrimination: (re)-introducing coefficient δ

Background: Questionnaires are used routinely in clinical research to measure health status and quality of life. Questionnaire measurements are traditionally formally assessed by indices of reliability (the degree of measurement error) and validity (the extent to which the questionnaire measures what it is supposed to measure). Neither of these indices assesses the degree to which the questionnaire is able to discriminate between individuals, an important aspect of measurement. This paper introduces and extends an existing index of a questionnaire's ability to distinguish between individuals, that is, the questionnaire's discrimination. Methods: Ferguson (1949) [1] derived an index of test discrimination, coefficient δ, for psychometric tests with dichotomous (correct/incorrect) items. In this paper a general form of the formula, δ G , is derived for the more general class of questionnaires allowing for several response choices. The calculation and characteristics of δ G are then demonstrated using questionnaire data (GHQ-12) from 2003–2004 British Household Panel Survey (N = 14761). Coefficients for reliability (α) and discrimination (δ G ) are computed for two commonly-used GHQ-12 coding methods: dichotomous coding and four-point Likert-type coding. Results: Both scoring methods were reliable (α > 0.88). However, δ G was substantially lower (0.73) for the dichotomous coding of the GHQ-12 than for the Likert-type method (δ G = 0.96), indicating that the dichotomous coding, although reliable, failed to discriminate between individuals. Conclusion: Coefficient δ G was shown to have decisive utility in distinguishing between the cross-sectional discrimination of two equally reliable scoring methods. Ferguson's δ has been neglected in discussions of questionnaire design and performance, perhaps because it has not been implemented in software and was restricted to questionnaires with dichotomous items, which are rare in health care research. It is suggested that the more general formula introduced here is reported as δ G , to avoid the implication that items are dichotomously coded

A Renewable Energy Plan for Mozambique

Mozambique has among the lowest uses of electricity in the world. Yet virtually all of the electricity it does produce from Cahora Bassa Dam on the Zambezi is shipped to its wealthy neighbor, South Africa. As the government prepares to build another costly large dam on the Zambezi that will also power South Africa rather than homes and businesses in Mozambique, a new report lays out a saner plan for developing renewable energy sources across the nation that would share the energy wealth more equitably; diversify the national electricity grid to help the nation adapt to climate change (which is expected to significantly affect large hydro), and build a clean energy sector that would also spare the Zambezi

Discrimination and reliability: equal partners? Understanding the role of discriminative instruments in HRQoL research: can Ferguson's Delta help? A response

A response to Norman GR 'Discrimination and reliability: equal partners?' and Wyrwich KW 'Understanding the role of discriminative instruments in HRQoL research: can Ferguson's Delta help?

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There are no author-identified significant results in this report

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Development and testing of the Rho Sigma Incorporated microprocessor control subsystem

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