Representativeness and Response Rates from the Domestic/International Gastroenterology Surveillance Study (DIGEST)

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Abstract
BACKGROUND: The Domestic/international Gastroenterology Surveillance Study (DIGEST) examined the prevalence of upper gastrointestinal symptoms among the general population in 10 countries, and the impact of these symptoms on healthcare usage and quality of life. This report discusses the validation of the DIGEST sample and reviews the response rates from the survey. METHODS: External validation of the DIGEST sample was conducted by comparing the age, age by gender and annual household incomes of the sample with census-derived data. A comparison was also made between Psychological General Well-Being Index (PGWBI) scores from study subjects in the Scandinavian countries and the USA and the total sample population norms. RESULTS: Under- and oversampling, defined as > or =5% difference from the population norms, was evident in eight out of 10 countries, but no systematic bias was evident. The final distribution of the sample by gender was 51% female and 49% male. Although differences in PGWBI scores were noted between DIGEST subjects and population norms, these differences were <0.30 standard deviations--markedly below the difference considered as relevant for the PGWBI. Response for the survey in individual countries ranged from 17% in the USA to 61% in Norway, with a survey-wide rate of 27%. The overall response rate, including primary non-respondents, was 13.4%. The majority of nonresponse (51.4%) was attributed to failure to establish contact with the subjects, with 41.7% of subjects declining to be interviewed and the remaining 6.9% of subjects not meeting the age and sex criteria used for the survey. CONCLUSIONS: The DIGEST sample exhibited good external validity, providing a foundation for comparison between data derived from individual countries in the surve