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CASE-CONTROL STUDY

CASE-CONTROL STUDY. CASE-CONTROL STUDY. Obseravational and analytical studies Longitudinal studies We start knowing the effect ( the disease ) and we look for the risk factor/factors, in general, in a retrospective manner Case-control study types : prospective retrospective.

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CASE-CONTROL STUDY

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  1. CASE-CONTROL STUDY

  2. CASE-CONTROL STUDY • Obseravational and analytical studies • Longitudinal studies • We start knowing the effect (the disease) and we look for the risk factor/factors, in general, in a retrospective manner • Case-control study types: • prospective • retrospective

  3. CASE-CONTROL STUDY The design of thecase-control study exposed Sample with disease unexposed Target population exposed Sample without disease unexposed Time Study direction

  4. CASE-CONTROL STUDY • Selecting disease cases: patients from a hospital or a medical service • Selecting the control group: • hospitalized patientssuffering from another disease • general population from the same town • specific groups (family, friends)

  5. CASE-CONTROL STUDY Sampling in case-control studies: • Random sample (by chance) • Systematic sample • Stratified sample

  6. CASE-CONTROL STUDY The data is organised into a 2x2 contingency table

  7. CASE-CONTROL STUDY DATA ANALYSIS • Exposure odds calculationfor both case and control groups: - exposure odds for cases = - exposure odds for control group = • ODDS RATIO (OR) =

  8. CASE-CONTROL STUDY INTERPRETATION OR > 1 there is an associationbetween exposure and disease OR = 1 there is NO associationbetween exposure and disease OR < 1

  9. CASE-CONTROL STUDY STATISTICAL ANALYSIS FOR CASE-CONTROL STUDIES • The appropriate statistical test is Chi² test • If the obtained “p” value is smaller than 0,05 (p<0.05) then we have a statistically significant result • CI – must not contain the value 1 (lower limit should be greater than 2)

  10. CASE-CONTROL STUDY OR interpretation depending onCI: • If OR>1 and CI limits are close to OR, but without including the value 1, then we can state that there is a positive association between the risk factor and the disease • If OR>1 and CI includes the value 1 we can say that is NO associationbetween exposure and disease

  11. CASE-CONTROL STUDY ADVANTAGES: • Fast • Cheap • Easy to perform • Requires a relatively small number of subjects • It looks into more than one risk factor (more than one exposure) • Suitable for rare diseases, with a high latency period • They can determine causality, they are usefullfor only one disease

  12. CASE-CONTROL STUDY DISADVANTAGES: • Memory errors, selection errors • It doesn’t allow a direct calculation of incidence • Data validation is difficult to determine • Thay can’t be used for rare exposures • They study only one effect

  13. CASE-CONTROL STUDY EXAMPLE: In an obstetrics clinic there was performed a study on the newborns between 1960 and 2000, in order to establish a possible connection between drinking alcohol during pregnancy and the apparition of the lip and maxillary cleft.During this study there were devised two groups, one of 43 newborns with lip clefs or labio-maxillo-palatine clefs and a control group with newborns without the malformation. There are no differences between the two groups (except the presence of the malformation in the cases group). There were excluded from the sample lot the patients with other malformations besides lip clefs or labio-maxillo-palatine clefs.

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