Study designs Wilfried Karmaus Reproductive Epidemiology EPI 824

Five basic study designs Descriptive study Descriptive study Cross-sectional study Cross-sectional study Longitudinal study and intervention trial Longitudinal study and intervention trial Case-control study Case-control study Aggregative study (ecological study) Aggregative study (ecological study)

Descriptive Studies (1) Descriptive studies examine the distribution of disease in a defined population. Based on existing mortality or morbidity statistics, such as hospital discharge data. Examine patterns of health outcome by age, gender or ethnicity, for specified time period or geographical areas. Estimates the incidence or prevalence of the disease: –Life time prevalence –Period prevalence –Point prevalence

Descriptive Studies (2) Do not formally evaluate the association between exposure and health outcome, although they can be helpful in assessing the possibility that an association exists. Descriptive data are used to examine patters of health outcome by: –Place –Time –Person

analytical observational studies randomized clinical or intervention trials Assumptions: knowledge about the appropriate time window of exposure & effect Flow of knowledge and its application

Cross-sectional study Begin of the studyMeasure/Classify and Compare Risk/Factor (+) Risk/Factor (-) Risk/Factor (+) Risk/Factor (-) Study population Free of Disease/Outcome Have Disease/Outcome

Sampling strategies for cross-sectional studies

Longitudinal study & intervention trials Begin of the studyMeasure/Classify the exposure Study population Free of Disease/Outcome Have Disease/Outcome Free of Disease/Outcome Have Disease/Outcome Risk/Factor (+) Risk/Factor (-) Disease- free at the beginning Measure and compare the disease frequency Change the exposure in an intervention trial

Case-control studies (case comparison, case referent) Caseness = starting point of case-control studies (medical care) Caseness = starting point of case-control studies (medical care) exposed not exposed No estimates of incidence or prevalence Cases exposed not exposed Controls Measure and compare the EXPOSURE frequency

Aggregative Study (ecological study) Mean of a variable Association? =aggregated data

Imagine some hypothesis for reproductive health outcomes (see below) and then develop some designs  age at menarche  age at menopause  age at first intercourse  interval between menarche and first intercourse  age at first marriage  cycle length, duration of menstruation  gestational age  LMP (date of last menstrual period before conception)  Time to pregnancy (TTP)  Periods of unprotected intercourse not leading to pregnancy (PUNP)  Contraceptive use  Planning a baby  Frequency of sexual intercourse  Number and gender of partners  Use of fertility services  Gravidity, Parity  Male or female infertility  Plurality  Pregnancy outcome: stillbirth, live birth, induced abortion, miscarriage, ectopic pregnancy  Gender of the offspring  Number of children  Fetal growth (ultrasound)  breech / cephalic delivery  birth weight, size, head circumference  placental markers  malformations  retinopathy of prematurity  fibroids, neoplasm  genital and breast development (Tanner stages)  sperm count / motility  AFP, etc.  pregnancy test  male and female hormone profiles