Wilfried Karmaus

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Study designs
Wilfried Karmaus Reproductive Epidemiology EPI
824
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Five basic study designs

• Descriptive study
• Cross-sectional study
• Longitudinal study and intervention trial
• Case-control study
• Aggregative study (ecological study)

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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

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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

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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
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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 (-)
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Sampling strategies for cross-sectional studies
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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
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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
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Aggregative Study (ecological study)
Mean of a variable
Mean of a variable
aggregated data
aggregated data
Association?
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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