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EPI 824 Reproductive outcomes. Wilfried Karmaus Department of Epidemiology, MSU karmaus@msu.edu You find class material in: http://www.msu.edu/course/epi/824/. Content. Scales Incidence, point / period / lifetime prevalence Sources of information Methods of determination

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Epi 824 reproductive outcomes l.jpg
EPI 824 Reproductive outcomes

Wilfried Karmaus

Department of Epidemiology, MSU

karmaus@msu.edu

You find class material in:

http://www.msu.edu/course/epi/824/


Content l.jpg
Content

  • Scales

  • Incidence, point / period / lifetime prevalence

  • Sources of information

  • Methods of determination

  • Reproductive markers (outcomes)

    • Time-related

    • Variable or stable characteristic

  • Validity and reproducibility


Epidemiology bridge between natural an social science and statistical models l.jpg
Epidemiology = Bridge between natural an social science and statistical models

Science to describe distribution of health and its risk factors in a population

Natural and social science

Statistical models that describe different distribution


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Scales statistical models

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”

  • Nominal scale (no inherent order)

  • Ordinal scale

  • Continuous scale (interval scale, ratio scale, discrete data [counts] )


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Sources of information statistical models

  • 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: http://www.mdch.state.mi.us/pha/osr/index.asp for: Jacobs Institute of Womens Health: http://www.jiwh.org)


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Methods of determination statistical models

  • 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.


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Reproductive outcomes (markers) statistical models

  • 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


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Reproductive outcomes (markers) statistical models

  • 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)


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Reproductive outcomes (markers) statistical models

  • Behavioral markers

    • Contraceptive use

    • Planning a baby

    • Frequency of sexual intercourse

    • Number and gender of partners

    • Use of fertility services


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Reproductive outcomes (markers) statistical models

  • Pregnancy characteristics / reproductive history

    • Gravidity

    • Parity

    • Plurality

    • Pregnancy outcome (stillbirth, live birth, induced abortion, miscarriage, ectopic pregnancy, etc.)

    • Gender of the offspring

    • Number of children


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Reproductive outcomes (markers) statistical models

  • Clinical 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.


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Reproductive outcomes (markers) statistical models

  • Biochemical characteristics

    Male:

    • hormones

    • sperm count / motility

      Female:

    • hormones

    • AFP, etc.

      Pregnancy:

    • pregnancy test, hormone profiles

    • immunological markers, RH-, ABO-system

    • bilirubin, etc.


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Validity and Reliability statistical models

  • 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:

    We compare two or more proxy-measurements or two or more determination of the gold standard.


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result of the test statistical models

disease

no disease

disease

a=true positive

b=false positive

no disease

c=false negative

d=true negative

Assessment of validity of a measurement

Truth

positive predictive value=a/(a+b)

negative predictive value = d/(c+d)

Sensitivity =

Pr(classified diseasedtruly diseased)

= a/(a + c)

Specificity =

Pr(classified non-diseased

truly non diseased)

= d/(b + d)


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Validity of a measurement statistical models

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).


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OBSERVATION A statistical models

abnormal

normal

OBSERVATIONB

abnormal

a

b

row1

normal

c

d

row2

col1

col2

total

Reproducibility of a measurement = Reliability

Comparing measurements, not with a gold standard.

  • Inter-rater (between observer)

  • Intra-rater (test – retest, within observer)


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Reproducibility of a measurement statistical models

·Discrete variables: kappa coefficient ·Continuous variables: intra-class correlation coefficient (ICC)

perfect agreement: kappa = 1

chance agreement: kappa = 0


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Take home points statistical models

  • 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.