Download to read offline
![Selection of Cases
The Specifications
Diagnostic Criteria
Eligibility Criteria
Only newly Diagnosed [Incident]
cases within a specified period of
time are eligible than old cases or
cases in advanced stage of disease
[Prevalent cases].](https://image.slidesharecdn.com/c03p06casecontrolstudy-230806063229-b36551f2/75/C03-P06-CASE-CONTROL-STUDY-ppt-8-2048.jpg)
![Matching
Matching is a comparative
technique of neutralising
all other variables present
in cases and controls,
except the variable
[Disease] under study, to
eliminate the systematic
errors [biases] while
conducting the study.
Group matching
Matching in pairs](https://image.slidesharecdn.com/c03p06casecontrolstudy-230806063229-b36551f2/75/C03-P06-CASE-CONTROL-STUDY-ppt-13-2048.jpg)
![Odds Ratio
Odds of exposure in cases:
A / C
Odds of exposure in controls:
B / D
Odds ratio:
[A / C] / [B/ D)]
Odds ratio:
AD / BC](https://image.slidesharecdn.com/c03p06casecontrolstudy-230806063229-b36551f2/75/C03-P06-CASE-CONTROL-STUDY-ppt-20-2048.jpg)
C03 P06 CASE CONTROL STUDY.ppt
- 1.
- 2. Definition CASE CONTROL STUDYIS AN ANALYTICAL AND COMPARATIVE METHOD OF OBSERVATIONAL NATURE TO TEST THE CAUSAL HYPOTHESIS. To establish causal association & its strength Purpose
- 3.
- 6. Types of CaseControl Study Unmatched Case Control Study Matched Case Control Study Nested Case Control Study
- 7. Basic Steps Selection ofCases and Controls Matching Measurement of exposure Analysis and Interpretation
- 8. Selection of Cases TheSpecifications Diagnostic Criteria Eligibility Criteria Only newly Diagnosed [Incident] cases within a specified period of time are eligible than old cases or cases in advanced stage of disease [Prevalent cases].
- 9. Sources of Cases Hospitals Generalpopulation The cases should be representative of all cases in the community.
- 10. 1. The prevalenceof exposure among controls should reflect the prevalence of exposure in the source population. 2. Controls should come from the same source population as cases (e.g. would have been cases if diagnosed with the disease). Selection of Controls
- 11. 3. The timeduring which a subject is eligible to be a control should be the time in which the individual is also eligible to be a case. If #1, #2, or #3 are not met = Selection Bias Selection of Controls
- 12. Sources of Controls HospitalControls Relatives Neighborhood Controls General population Random digit dialing AXIOM: The benefit of increased sample size is not as relevant past the 1:4 ratio (e.g increase in statistical power).
- 13. Matching Matching is acomparative technique of neutralising all other variables present in cases and controls, except the variable [Disease] under study, to eliminate the systematic errors [biases] while conducting the study. Group matching Matching in pairs
- 14. Matching Advantages Disadvantages May increasethe precision of case-control comparisons and thus allow a smaller study May be time-consuming and expensive to perform The sampling process is easy to understand and explain Some potential cases and controls may be excluded because matches cannot be made If analyzed correctly, provides reassurance that matched variables cannot explain case-control differences in the risk factor of interest The matched variables cannot be evaluated as risk factors in the study population
- 15. Confounding is a distortionof results that occurs when the apparent effects of the exposure of interest are attributable entirely or in part to the effects of an extraneous variable. Example.age Confounding factors
- 16.
- 17. Measurement of exposure By Interviews Questionnaires Pastrecords Hospital records Employment records etc.
- 18.
- 19. Unmatched Case Control Datais expressed in a four- fold table, and an odds ratio is calculated Cases Controls Exposed a b Unexposed c d Odds Ratio = ad/bc
- 20. Odds Ratio Odds ofexposure in cases: A / C Odds of exposure in controls: B / D Odds ratio: [A / C] / [B/ D)] Odds ratio: AD / BC
- 21. Case Control E E EE E N E N E N E N N E N N N N Case Control Exposed Not exposed 6 3 4 7 Odds ratio = 6/4 =3.5 3/7 Odds ratio in unmatched case-control
- 22. Odds Ratio inMatched Case Control Concordant pairs Both case and control were exposed Neither case nor control were exposed Discordant pairs Case exposed but control not exposed Case not exposed but control exposed
- 23. Cont.. Odds Ratio =Ratio of Discordant pair = b/c Exposed Not exposed Exposed a b Not exposed c d Control Case
- 24. Matched Case-Control Studyof Association Between Use of Oral Conjugated Estrogens and Cervical Cancer Estrogen Use Present Absent Total Present 12 43 55 Absent 7 121 128 Total 19 164 183 • OR=43/7=6.14
- 25. Interpretation OR > 1indicates a positive association between the factor and the disease. OR < 1 indicates the factor is protective OR = 1 indicates no association
- 26. Bias Confounding bias Memory bias Selectionbias Berkesonian bias Interviewer's bias
- 27. Advantages Quick and Inexpensive Optimalfor rare diseases Useful for diseases of long latency from exposure to disease development Can evaluate multiple risk factors
- 28. Disadvantages Cannot calculate incidence rate Notsuited for rare exposures May not elucidate temporal sequence of exposure and disease Susceptible to bias (selection & recall)
- 29. Examples of CaseControl Study Doll’s 1951 study of smoking and lung cancer. Doll
- 30. Male lung cancer patients Malepatients other diseases Smokers 647 (99.7%) 622 (95.8%) Nonsmokers 2 27 Total 649 649 OR = 647 x 27 = 14.04 622 x 2 Doll and Hill’s Data
- 31. Thalidomide tragedy A retrospectivestudy of 46 mothers who delivered deformed babies were found to have Thalidomide during their early pregnancy.This was compared with a control of 300 mothers who delivered normal babies.
- 32. Cont…. 1950’s Cigarette smoking andlung cancer 1970’s Diethyl stilbestrol and vaginal adenocarcinoma Post-menopausal estrogens and endometrial cancer
- 33. Cont…. 1980’s Aspirin andReyes syndrome Tampon use and toxic shocks syndrome L-tryptophan and eosinophilia- myalgia syndrome AIDS and sexual practices 1990’s o Vaccine effectiveness o Diet and cancer
- 35. Nested case-control studies arecase-control studies done in the population of an ongoing cohort study. The case-control study is thus said to be “nested” inside the cohort study. NESTED CASE CONTROL STUDIES
- 36. TIME 1 YEARS TIME 2 StudyPopulation Develop Disease Do Not Develop Disease CASES CONTROLS CASE-CONTROL STUDY Obtain interviews, bloods, urines, etc. Nested Case-Control Studies
- 37. How is itpossible to measure the exposure retroactively in a cohort study? Usually when the following situations occur: A specimen (e.g. of blood) had been stored but not analyzed. An interview is conducted to ask about at an exposure not assessed at baseline Records of exposure (medical records, occupational records) are retrieved that were not thought about when the cohort was first assembled NESTED CASE-CONTROL
- 38. Analysis is justlike any case-control study with computation of an odds- ratio, adjustment for confounding, etc. NESTED CASE-CONTROL
- 39. Example In ARIC (AtherosclerosisRisk in Communities) study, a cohort of 16 thousand men, all men provided serum samples at the outset which were saved. The cohort is observed for CHD. After 5 years we have 246 cases of CHD. We randomly choose 500 participants to be controls. We only measure Chlamydia antibody in the stored sera from these 246 + 500 subjects. We compare the cases (CHD) to the controls (no CHD) with regard to the presence of exposure (Chlamydia) which preceded the outcome.
- 40. Reference K.Park-T.B of P.S.M.. Mahajan– T.B. of P.S.M W.H.O – Basic Epidemiology Oxford – T.B. of Public Health Mc.Graw Hill www.pubmed.gov www.cdc.gov www.who.int