Wiggins, Richard D
(1990)
A methodological investigation of non sampling error: Interviewer variability and non response.
PhD thesis, London School of Economics and Political Science.
Abstract
Two principal sources of error in data collected from structured interviews with respondents are the methods of observation itself, and the impact of failure to obtain responses from selected individuals. Methodological strategies are developed to investigate practical ways of handling these errors for data appraisal. In part one, the differential impact of each of a group of interviewers on the responses obtained in two separate epidemiological studies is examined. Interviewer effect is measured and its impact on the interpretation of individual responses, scale scores and modelling is shown. The analysis demonstrates that it is possible to achieve four objectives with slight modification of survey design. First, estimates of precision for the survey results can be improved by including the component due to interviewer variability. Secondly, items with high sensitivity to interviewer effect can be identified. Thirdly, the pattern of distortion for different types of items can be discovered. Replicate analyses appear to indicate that deviations between interviewers are not always consistent over time. Fourthly, by means of 'variance component modelling' the presence of interviewers on the interpretation of linear models can be evaluated. These models are used to show how interviewer characteristics may be used to account for variation in the responses. Part two establishes an evaluative framework for the systematic review of interviewer call back strategies in terms of nonresponse bias and the costs of data collection. Use of an 'efficiency index', based on a product of 'mean square error' and cost for items in a survey of occupational mobility provides a retrospective evaluation. The empirical evidence had important practical consequences for fieldwork. The possibility of alternative call-back norms and the relative efficacy of appointment versus non-appointment calls is shown. The methodology develops from a review of adjustment procedures for nonresponse bias and models for survey costing. Logically, the methodologies for the three empirical investigations could be combined into an appraisal for a single survey. Only lack of resources inhibited such an outcome.
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