Published on March 12, 2014
By Dr Aijaz Ahmed Sohag Prep by: Abdul Wasay Baloch Amna Inayat Medical College Case Control vs Cohort Control
Case Control Cohort Control Proceeds from effect to cause Starts with the disease To know suspected cause occurs more frquently having disease than those without disease Suitable for study of Rare disease Relative inexpensive Proceeds from cause to effect Starts with exposure To know whether disease occur more frequently in those exposed to risk factors(a+b) than non exposed (c+d) Suitable for exposure of Rare response Comparatively expensive Case Control Cohort Control
Generally yields only estimate risks (odds ratio) Time of study relatively short Population size needed relatively small Potential bias larger (assessment of exposure) Generally yeilds relative risk, attributable Risk, besides incidence rate Relatively large Comparatively mimic less (assessment of outcomes) E.g. Smoking and lung cancer. Fermingham heart study, Oral contraceptive and health Case Control Cohort Control
RR estimate may increase or decrease as a result of bias a) Bias due to confounding (may be reduced by Matching) b) Memory or Recall bias c) Selection bias d) Berkesonian bias or Joseph bias e) Interviewer bias (may be reduced by double blinding) Examples Adenocarcinoma of Vagina Oral contraceptive and thromboemolic disease Thalidomide tragedy Ethical problems minimal Incidence can not be measured, and can only estimate the Relative Risk
Incidence Rate Cigrette smoking Developed Lung cancer Did Not Develop Lung cancer Total Yes 70 (a) 6930 (b) 7000 (a+b) No 3 (C ) 2997(D) 3000 (c+d)
Incidence Rate among Smokers a/(a+b) = 70/7000*1000 = 10 per 1000 Among Non- smokers = c/(c+d)= 3/3000*1000 = 1 per 1000 Estimation of Risk: Relative risk = incidence of dis among exposed/incidence of dis among non expose= RR = 10/1=10 Attributable risk= incidence of dis among exposed – incidence of disease among non exposed/incidence rate among exposed =10-1/10 *100 = 90%
RR AR To study etiology (cause) it has an edge over AR It measure Strength of association between suspected cause and effect Larger the RR, stronger the association between Cause and Effect. RR 1 indicates no association RR has less public health importance as does RR E.g. if RR is 10, it means smokers are 10 times at greater risk of developing lung cancer than non smokers. Comparatively AR has less importance studying antilogy of disease It measures To What extent disease under study Attributed to exposure e.g. 90 % lung cancer in smokers was due to smoking AR gives better idea than does RR of the impact of preventive/public health program in reducing problem
sequently revised during ... sions with the larger group of STROBE con- ... Observational studies · Cohort studies · Case-control studies ...
(Received in revised form 29 June 1989) ... A case-cohort approach is applied, ... Apart from sampling and follow-up con-
In ancient times, a cohort was a military unit, one of ten divisions in a Roman legion. The term passed into English via French in the 15th century, when ...
An introduction to risk set based ... methods for cohort and case-control studies as well as between ... as well as the appropriate variance and con -
... Revised 29 December 2011 ... the speciﬁc situations of case-cohort and nested case ... which is here con-sidered as the baseline of the cohort, ...
Observational research methods––Cohort studies, cross sectional studies, and case ... revised 22 December 2011 ... Cohort, cross sectional, and case ...
... A Cohort Analysis ... this paper do not incorporate recently revised NIPA data for the years starting in 1959. ... in the case of health care, ...
Evolution of epidemiologic methods and concepts in selected ... A revised version of these ... study designs (cohort studies and case-con-trol studies) ...
in Matched Case-Control Studies with Categorical Exposure ... such as case-control, case-cohort, ... in epidemiologic designs to control the effects of con-