Question

1. Match the following excerpts with the appropriate epidemiologic study design. (Study design may be used more than once or none at all.) (8 points)

Excerpt	Study Design
____ Conduct one telephone interview with a random sample of 2,000 women who gave birth in Hillsborough County anytime during 1998. Question the women about any congenital birth defects in their babies born during 1998 and on whether they were exposed to cigarette smoke during the first trimester of their pregnancy.	Case-Control Cross-Sectional Ecological Prospective Cohort Retrospective Cohort
____ In a population-based study using the regional cancer registry, the investigators aimed to examine whether residents of the area around Schiphol-Airport are at higher risk of developing cancer than the general Dutch population. They estimated the cancer incidence during 1988-2003 in residents of the area surrounding Schiphol-Airport and defined a study area based on aircraft noise contours and 4-digit postal code areas, since historical data on ambient air pollution were not available and recent emission data did not differ from the background urban air quality.
____ To assess the possible carcinogenic effects of radio-frequency signals emitted by cellular telephones, an investigator conducted a study in Denmark. The two companies that operate cellular telephone networks in Denmark furnished names and addresses for all 522,914 of their individual clients during the years from 1982 – 1995. The investigators then matched these records to the Danish Central Population Register, which contains a unique 10-digit number for each person and information on vital status and emigration. After removing non-matches, duplicates, persons outside the study’s age limits or geographic catchment area, and persons who asked not to be studied, 420,095 cellular telephone subscribers remained and formed the exposed cohort. The resulting data allowed calculation of cancer incidence rates (using existing vital status data in the Register) for the exposed and unexposed cohorts.
____ Using 1997 Tampa General’s nursery discharge records, identify a random sample of 50 babies born with congenital birth defects and a random sample of 200 babies born without congenital birth defects. Interview each mother over the phone, asking about exposure to video display terminals during the first trimester of pregnancy.

Answer 1

Answer:1 - Retrospective Cohort

Explanation:

1. The investigator has selected a cohort - women who gave birth to babies with congenital anomalies
2. Later he tries to go back in time to study whether they were exposed to the risk factor (cigarette smoke during 1st trimester)

Answer:2 - An ecological study

Here the study population is studied as a whole and not as individual.

Answer:3 - Prospective cohort study

Explanation:

1. The investigator identified 2 cohorts
2. They had exposure to radiofrequency signals (risk factor)
3. One cohort was not exposed to the risk factor the other was
4. they were followed up to the present day and the cancer incidence between the exposed and the non exposed was calculated.

Answer: 4 - Case-control study -

Explanation

1. The investigator first identifies an outcome ( birth defects).
2. Next, identifies two groups of women, one with babies with birth defect( outcome) and ones without birth defect ( without the outcome)
3. Later the investigator asks these mothers about the history of exposure to a risk factor ( video display terminals during the first trimester)
4. This is called case-control study.