Wilfried Karmaus Department of Epidemiology, MSU You find class material in: EPI 824 Reproductive outcomes

Content 1.Scales 2.Incidence, point / period / lifetime prevalence 3.Sources of information 4.Methods of determination 5.Reproductive markers (outcomes) a.Time-related b.Variable or stable characteristic 6.Validity and reproducibility

Epidemiology = Bridge between natural an social science and statistical models Natural and social science Statistical models that describe different distribution Science to describe distribution of health and its risk factors in a population

Scales Nominal scale (no inherent order) Ordinal scale Continuous scale (interval scale, ratio scale, discrete data [counts] ) Epidemiologic measures Incidence = change of status over time = rate (time is in the denominator) Prevalence = proportion = risk Point prevalence (on this day etc., in this exam) Period prevalence (in the last 3 months, 12 months, etc. Life time prevalence: “ever experienced”

Sources of information Collection of new data (interviews, clinical, blood, human milk, placenta, amniotic fluid, etc.) Files (medical files, company files, etc.) Public records (birth registry, natality statistics, grave yards, birth defects, for Michigan: for: Jacobs Institute of Womens Health:

Methods of determination Interviews, questionnaires Abstract existing files Clinical investigations: breech or cephalic presentation, malformations, birth weight, head circumference, ultrasound examinations, etc. Biochemical measurements: hormones, AFP, pregnancy tests, etc.

Reproductive outcomes (markers) Time-related markers  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

Reproductive outcomes (markers) Time-related markers  gestational age  LMP (date of last menstrual period before conception)  Time to pregnancy (TTP)  Periods of unprotected TUI intercourse not leading to (time of pregnancy (PUNP) unprotected intercourse) (time of unprotected intercourse)

Reproductive outcomes (markers) Behavioral markersBehavioral markers  Contraceptive use  Planning a baby  Frequency of sexual intercourse  Number and gender of partners  Use of fertility services

Reproductive outcomes (markers) Pregnancy characteristics / reproductive historyPregnancy characteristics / reproductive history  Gravidity  Parity  Plurality  Pregnancy outcome (stillbirth, live birth, induced abortion, miscarriage, ectopic pregnancy, etc.)  Gender of the offspring  Number of children

Reproductive outcomes (markers) Clinical characteristicsClinical characteristics  Fetal growth (ultrasound)  breech / cephalic delivery  birthweight, size, head circumference  placental markers  malformations  retinopathy of prematurity  fibroids, neoplasm  genital and breast development (Tanner stages)  variocele, PID, etc.

Reproductive outcomes (markers) Biochemical characteristicsBiochemical characteristicsMale:  hormones  sperm count / motility Female:  hormones  AFP, etc. Pregnancy:  pregnancy test, hormone profiles  immunological markers, RH-, ABO-system  bilirubin, etc.

Validity and Reliability Validity of a measurement: We have a gold standard.Validity of a measurement: We have a gold standard. –Pap smear and biopsy –Circumcision status and physician’s examination by questionnaire Reliability or reproducibility of a measurement:Reliability or reproducibility of a measurement: We compare two or more proxy-measurements or two or more determination of the gold standard. We compare two or more proxy-measurements or two or more determination of the gold standard.

result of the test diseaseno disease disease a=true positive b=false positive no disease c=false negative d=true negative positive predictive value=a/(a+b) negative predictive value = d/(c+d) Specificity = Pr(classified non-diseased  truly non diseased) = d/(b + d) Sensitivity = Pr(classified diseased  truly diseased) = a/(a + c) Truth Assessment of validity of a measurement

Validity of a measurement criteria: - specificity and - sensitivity Sensitive tests: high detection rate of persons truly diseased (or truly exposed) Specific tests: high detection rate of persons free of disease (or free of exposure) Sensitivity and specificity of a test are independent of the prevalence of the disease (exposure).

OBSERVATION A abnormalnormal OBSERVATION B abnormalabrow1 normalcdrow2 col1col2total Reproducibility of a measurement = Reliability Comparing measurements, not with a gold standard. Inter-rater (between observer) Intra-rater (test – retest, within observer)

Reproducibility of a measurement  Discrete variables: kappa coefficient  Continuous variables:intra-class correlation coefficient (ICC) perfect agreement: kappa = 1 chance agreement: kappa = 0

Take home points Reproductive epidemiology uses a wide range of measurement methods. Time-related measurements are common variables in reproductive epidemiology. We cannot not easily express all variables as incidence or prevalence. Questionnaires and registry data are frequently applied to determine the burden of health problems. Specific and more costly procedures are used to determine the etiology of adverse outcomes in smaller samples.