Many scientific studies of dietary health effects are observational. compared to experimental studies, observational studies can extend over a longer time period, use a more representative population, and measure disease outcomes in addition to risk factors for disease.
in an observational study, researchers enlist a study group, and use questionnaires and medical tests to quantify participants' health behaviors and status at the start of the study. the researchers continue to collect data on the participants over many years. information about each particpant's diet, lifestyle habits, risk factors, and disease outcomes are all recorded and analyzed.
a landmark study of this type -- called the nurses' health study -- was begun in 1976 with more than 120,000 female nurses. data from a subset of this group (80,082 women) was used to study dietary fat intake from 1980 to 1994. one goal of that study was to measure the effect of dietary trans fats on cardiovascular health.
do you understand how the nurses health observational study of dietary fats was set up and carried out?
sort the statements into the appropriate bins depending on whether they represent factors that varied from participant to participant at the start of this study, factors that were consistent from the start of the study, and factors that were measured in the study.