Part 1. Describe the distinctive features of case control studies. cohort studies, and intervention studies. 
Part 2. Decide which type of study was used to determine the cause of an outbreak in Brazil. 
An outbreak of microcephaly occurred in infants in 2015. Microcephaly is a condition of abnormally small heads and
results in severe brain damage in the affected infants. The cause was not known. Epidemiologists considered three hypotheses:

Mother’s exposure to a larvacide to control mosquito population
Use of Tdap vaccine for tetanus, diptheria, and pertussis in expectant mothers
Infection with zika vrus by the mother and fetus during preganancy

The study examined newborns with microcephaly from 8 hospitals compared to normal babies. Data was collected on all three types of exposure, andresults showed which of the hypotheses was correct. What type of test statistic would you use todemonstrate the group with the strongest association with microcephaly? How would you set up a ratio for each of the three groups and decide the correct hypothesis?