The effect of survey sampling frame on coverage: the level of and changes in alcohol-related mortality in Finland as a test case

Abstract

Exclusion of, for example, the homeless and institutionalized from survey sampling frames has been suggested to be one important reason for low coverage rate of surveys. We assess this, using mortality data from Finland, where in 2004 alcohol taxes were lowered by one-third, and surveys were unable to capture the 10% increase in per capita consumption.We compared the level of and the change in alcohol-related mortality in 2001-03 and 2004-05 in (1) the whole population, (2) the population included in the sampling frame of many Finnish surveys and (3) the population excluded from the sampling frame.Finns aged 15 years and above, linked individually to cause of death data.The population outside survey sampling frames constituted 1.4% of the whole population and had a high rate of alcohol-related deaths. For example, among men the rate of directly alcohol-attributable causes was 3.7 times higher than in the survey population. Among women the rate ratio was 4.6. The exclusion of the non-survey population reduced the estimated level of alcohol-related mortality by 1-4%. Similarly, the non-survey population had only a marginal effect on the estimates of temporal change.Alcohol-related mortality, and hence probably also alcohol consumption, is on average much higher in the subgroups of populations excluded from survey sampling frames. Due to the small size of the excluded group in the Finnish context, this has only a small effect on population-level estimates.