Читать книгу Statistics in Nutrition and Dietetics - Michael Nelson - Страница 30

Some studies are observational rather than experimental in nature. The purpose of these studies is often to help in the generation of hypotheses by looking in the data for relationships between different subgroups and between variables. Once the relationships have been described, it may be necessary to set up a new study which is designed to test a specific hypothesis and to establish causal relationships between the variables relating to exposure and outcome. For example, Ancel Keys observed that there was a strong association between the average amount of saturated fat consumed in a country and the rate of death from coronary heart disease: the more saturated fat consumed, the higher the death rate. Numerous studies were carried out subsequently to test the hypothesis that saturated fat causes heart disease. Some repeated Ancel Keys’ original design comparing values between countries, but with better use of the available data, including more countries. Other studies compared changes in saturated fat consumption over time with changes in coronary heart disease mortality. Yet other studies looked at the relationship between saturated fat consumption and risk of heart disease in individuals. Not all of the studies came to the same conclusions or supported the hypothesis. It took some time to understand why that was the case.