Case Control Studies.pptx

Epidemiology

1. Case Control Studies

2. Introduction Suppose you are a clinician and you have seen a few patients with a certain disease. You observe that many of them have been exposed to a particular agent—biological or chemical. You hypothesize that their exposure is related to their risk of developing this disease . How would you go about confirming or refuting your hypothesis ? Study designs!!!

3. CASE CONTROL Is an observational study in which the two existing groups differing in outcome (case and control) are identified and compared on the basis of some supposed causal attribute. S tudy of persons with the disease (or another outcome variable) of interest and a suitable control group of persons without the disease (comparison group, reference group) 4 .

4. Outcome----Exposure https:// kids.frontiersin.org/articles/10.3389/frym.2020.00015 .

5. Design Start with people who have disease(Cases) Match them with control that do not have the disease Measure past exposure Measure: interview or by review of medical or employee records or of results of chemical or biologic assays of blood, urine or tissues.

6. Design https://deakin.libguides.com/quantitative-study-designs/casecontrol

7. Design

8. Hypothetical Example-Case control W hether smoking is related to CHD . We start with 200 people with CHD (cases) and compare them to 400 people without CHD (controls) O f the 200 CHD cases, 112 were smokers and 88 were nonsmokers. Of the 400 controls, 176 were smokers and 224 were nonsmokers

9. Hypothetical Example-Case control… If there is a relationship between a lifetime history of smoking and CHD. Greater proportion of the CHD cases than of the controls would have been smokers (exposed) . Our example: 56% of CHD cases were smokers compared to 44% of the controls .

10. Sources of control group Non hospitalized OPD Inpatients admitted for diseases other than that for which the cases were admitted.

11. When to use it F irst step when searching for a cause of an adverse health outcome. Case-control studies are also valuable when the disease being investigated is rare. Out break Eg : In a study addressing the association of Guillain-Barré syndrome with Zika virus infection in French Polynesia in 2013–2014;Cao-Lormeau and colleagues noted that during the Zika outbreak, there was an increase in reports of Guillain-Barré syndrome suggestive of a possible relationship

12. Advantages G enerally less expensive-than cohort studies. C an be carried out more quickly. Case-control studies are also valuable when the disease being investigated is rare .

13. Disadvantages Potential for recall bias Potential for selection bias Can not establish risk Can not establish prevalence

14. Possible biases Selection bias -Sources of cases eg . Tertiary hospital -Using incident or prevalent case Preferable incident cases; any risk factors we may identify in a study using prevalent cases may be related more to survival with the disease than to the development of the disease (incidence) Information bias -Recall problems,two types: limitations in recall and recall bias

15. Info bias-Limitations in recall

16. Recall Bias Individuals with a particular disease tend to remember every detail of exposure they might have had that has led them to have the disease Eg.Study on covid 19 pt Vs non Covid 19 with exposure being in same room with a person coughing Those with cvd will remember more while those without might miss or not at all recall Ernst Wynder,a well-known epidemiologist, also called it “rumination bias.”

17. Summary CASE CONTROL What is it How to design Sources of control group When to use it Advantages/Disadvantages Biases

18. A case-control study is characterized by all of the following except : a. It is relatively inexpensive compared with most other epidemiologic study designs b. Patients with the disease (cases) are compared with persons without the disease (controls ) c. Incidence rates may be computed directly d. Assessment of past exposure may be biased e. Definition of cases may be difficult

19. References Deakin Univeristy Lirary . [Online] https://deakin.libguides.com/quantitative-study-designs/casecontrol . 2 . Frontiers for young Minds. [Online] https:// kids.frontiersin.org/articles/10.3389/frym.2020.00015 3. David , Moyses Szklo . Case control Studies. GORDIS EPIDEMIOLOGY, SIXTH EDITION. Philadelphia : Elyse O’Grady . 4 . Porta , Miquel . [book auth.] International Epidemiological Association. A dictionary of epidemiology 6th Edition. s.l . : International Epidemiological Association, Inc.

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