1. Study designs Wilfried Karmaus Reproductive Epidemiology EPI 824

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

3. 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

4. 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

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

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

8. Sampling strategies for cross-sectional studies

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

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

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

12. Imagine some hypothesis for reproductive health outcomes (see below) and then develop some designs • 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 • 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