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Study designs. Wilfried Karmaus Reproductive Epidemiology EPI 824. Five basic study designs. Descriptive study Cross-sectional study Longitudinal study and intervention trial Case-control study Aggregative study (ecological study). Descriptive Studies (1).

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Study designs

Wilfried Karmaus

Reproductive Epidemiology

EPI 824


Five basic study designs
Five basic study designs

  • Descriptive study

  • Cross-sectional study

  • Longitudinal study and intervention trial

  • Case-control study

  • Aggregative study (ecological study)


Descriptive studies 1
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
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


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


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 (-)



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


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


Aggregative Study (ecological study)

Mean of a variable

Mean of a variable

=aggregated data

=aggregated data

Association?


Imagine some hypothesis for reproductive health outcomes see below and then develop some designs
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


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