Читать книгу Statistics in Nutrition and Dietetics - Michael Nelson - Страница 44

Descriptive studies in epidemiology include ecological studies, cross‐sectional studies, and time trend analysis. They are useful for generating hypotheses. Measurements can be made in individuals at a given point in time (cross‐sectional studies) or accumulated over time in groups of people (ecological studies). They are used to relate measures of exposure and outcome in groups of people that share common characteristics (e.g. vegetarians versus omnivores) or to compare regions or countries. For example, they might compare diet and disease patterns between countries (are heart disease rates lower in countries where people eat lots of oily fish?) or between subgroups (do vegetarians have lower risk of heart disease compared to non‐vegetarians?).

There are two main problems with this type of study. First, there may be other factors that could explain an observed association or changes in the population over time. For example, populations with higher oily fish consumption may be more active or less obese. Second, not everyone in the population or subgroup is exposed at the same level: some individuals in the population may eat lots of oily fish, while others may eat very little. Are the people with low oily fish consumption the ones that have higher rates of heart disease?