Chapter 9 Notes

Cohort: Hypothesis-Exposure is associated with disease/outcome
ex: Smoking associated w/lung cancer
ex: access to Cinemax under age 12 associated w/risky sexual behavior age 21+

Case Control: Hypothesis-Disease is associated w/particular exposure.

Cohort vs Case Control

1. Choose population (cohort) to follow some people in cohort will be exposed to thing you think associated w/disease, others not (and so people in cohort as similar to each other as possible)
2. Track Cohort-record who develops disease and who doesn't
3. Calculate incidence of disease in exposed and not exposed groups and compare
*Prospective/longitudianl study: start now, track cohort into future
*Retrospective: start now, but w/old records to identify cohort then collect data on exposures and outcomes of cohort members
ex: Semmelweis-Cohort: women who delivered babies at kronkenhous Allemegre Retrospective Review of 2 yrs of maternal ward records. exposed=Dr. delivered babies, Nonexposed=Nurse/midwife delivered babies
Outcome=Death from puerper fever

Case Control
1. Select subjects who have a disease (cases)
2. Select subjects who dont have disease (controls) but otherwise similar
3. Collect data re: subjects' exposure to thing you think associated w/disease
4. Calculate and compare porportion of cases exposed to exposure and of controls exposure

Cohort Advantages: Track population over time and record new cases-measure incidence of outcome, which is a measurement of risk-case control since one group has disease and other group doesnt, you cant measure incidence/prevalence-cant measure risk

Case Control Study Advantages: Handier at looking at diseases that take a long time to develop or diseases that are rare.

***IF THERE IS NO COMPARISON GROUP, NO ASSOCIATION BETWEEN EXPOSURE AND DISEASE CAN BE MADE.-thats why cohorts/case controls are reliable and advantagous over case studies where there are no control/comparison group.

Framingham (pg 171): 30-62 yr olds in framingham alabama, MA 1948 follow to see whether heart disease develops.
Exposures defined: smoking, lack of physical activity, sugar diabetes, sweetie, i cut yo 2 fingaz into a million pieces, obesity.

Problems w/cohort Studies
*prospective-drop-outs;expenses;hypothesis can change while study is being conducted (b/c of new discoveries made btw beginning of study and conducting of study) so you may not have collected the right data
*Retrospective: Since records collected by other ppl, for other purposes, in past, may not include all reliable (relevant) info..

Set up Case Control Study

Selection of Cases: Issues
1. Incident-Disadvantages=hard to study rare diseases. Adv=More accurately looks at rish and can establish before and after relationship between exposure and disease
2. Prevalent Cases-Disadvantages=may uncover association between living w/disease and exposure, not between disease itself and exposure. Adv=easier to study rare diseases because you dont have to wait for disease to pop up before study.

Selection of Controls
-healthy controls: 1. neighborhood-pick close to cases. 2. Best Friend-relatives help control for genetic factors that contribute to disease. 3. Hospitalized Controls-ones who are sick, just not with your disease of study (easy to obtain but not necessarily representative of underlying population)

Control Match to Cases
1. Group Matching-Have casesfigure out characteristics you think its important to match on (ex: demographics) and calculate % cases w/characteristic-pick controls so % of people w/different characteristics match cases
ex: Cases: 75% male and 25% female so out of 100 controls pick 75 males and 25 females.

2. Matched Pairs-enroll case, enroll control matched for significant characteristics.
ex: Case 1: 45 yo, divorced, white female (disease)
Control 1: 45 yo, divorced, white female (no disease)

difficult to do and traits that you match cases and controls on cant be studied.

Problems w/finding Exposures w/interview/survery…1. people doent accurately know info 2. Recall Bias: people who have bad outcome more likely to remember prior events than people w/out bad outcome

Multiple Controls-1. greater than 1 control/case 2. losts of subjects which increases statistical power 3. cant increase # of cases much so can increase controls to increase subject #

Cross Sectional Study
-look at overal population and divide into people with disease and exposure, people without disease with exposure, people without disease and with exposure, people without disease without exposure.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License