tasoryhmät

Tasoryhmät is Finnish for strata or strata groups, referring to subdivisions within a population that are designed to be internally similar while differing from other groups. They are used to organize data, samples, or interventions so that each subgroup is represented and analyzed separately.

In statistics and survey design, tasoryhmät are central to stratified sampling. The population is partitioned into non-overlapping groups based on one or more variables, such as age, region, gender, income, or education. Within each stratum, samples are drawn, often proportionally to the stratum’s size. This approach can improve estimate precision and allow comparisons across subgroups. After data collection, weights may be adjusted to account for different selection probabilities across strata.

Characteristics of tasoryhmät include mutual exclusivity and collective exhaustiveness: every member of the population belongs to one and only one stratum, and all strata together cover the whole population. The choice of stratification variables should be relevant to the study objective, and the number and size of strata should balance the gain in precision with practical considerations such as sample size and field costs.

Beyond statistics, tasoryhmät are used in policy planning, market research, and health studies to tailor interventions, analyze subgroup differences, or target resources. They enable more granular insights than whole-population analyses and support comparisons across defined segments while maintaining overall representativeness.