OR Qs Flashcards
Interpret the above OR with the 95% CI
(OR Interpretation): Odds Ratio (OR) = (Odds of exposure in cases) /(Odds of exposure in controls) = (a/c) / (b/d) = ad / bc.
Interpretation: Children from the estate sector have 4.3 times the odds ofbeing undernourished compared to children from the rural sector. The95% Condence Interval (CI) is 3.2 - 5.7. Since the CI does not include 1.0,this association is statistically signicant at the p<0.05 level. Being fromthe estate sector appears
Advantages/Disadvantages of Case-Control
Advantages: Ecient for studying rare outcomes (if undernutrition wasrare), relatively quick and inexpensive, can study multiple exposures/riskfactors simultaneously, requires smaller sample size than cohort studies,good for diseases with long latency. (Com Med Notes, pg 63)
Disadvantages: Prone to selection bias (choice of cases/controls), prone■ to information bias (recall bias regarding exposures), cannot calculateincidence or RR directly, temporal relationship between exposure andoutcome can be dicult to establish, not suitable for rare exposures.(Com Med Notes, pg 64)
Risk factors for colon cancer:■ Study Design
Case-Control Study. Colon cancer can have a longlatency and may not be extremely common, making case-control ecient.Recruit colon cancer patients (cases) and controls, compare pastexposures (diet, family history, etc.). Alternatively, a Cohort Study(especially retrospective using existing records if available) could be usedbut would be more resource-intensive.
What is the first criterion for instituting a screening program?
The disease should be an important public health problem with high prevalence/incidence and serious consequences. It must have a recognizable latent or early symptomatic stage, and its natural history should be adequately understood.
What is the second criterion for instituting a screening program?
A suitable screening test must be available that is safe, acceptable to the population, accurate (valid with good sensitivity and specificity), reliable, and relatively inexpensive.
What is the third criterion for instituting a screening program?
Effective and acceptable treatment must be available for individuals identified with the disease in its early stage, leading to better outcomes than later treatment.
What is the fourth criterion for instituting a screening program?
Facilities for diagnosis and treatment must be available, and the cost of case-finding should be economically balanced in relation to medical care as a whole.
What should case-finding be considered in the context of a screening program?
Case-finding should be a continuous process, not a one-off project, with benefits outweighing the risks (physical, psychological, financial). There should be an agreed policy on whom to treat as patients.
What is the RCT?
RCT stands for Randomized Controlled Trial, which is considered the gold standard for interventions.
What are the advantages of RCTs?
RCTs minimize bias and confounding through randomization and blinding.
What are the disadvantages of RCTs?
RCTs can be expensive, face ethical constraints, and may lack generalizability.
What is Endemic?
The constant presence of a disease or infectious agent within a given geographic area or population group; may also refer to the usual prevalence of a given disease within such area or group. Baseline level.
(e.g., Malaria was endemic in parts of SL)
What is Epidemic?
The occurrence in a community or region of cases of an illness, specific health-related behaviour, or other health-related events clearly in excess of normal expectancy. A sudden increase above baseline.
(e.g., Dengue epidemics in SL)
What is Selection Bias?
Selection Bias occurs when cases or controls are not representative of the general population.
Examples include selecting cases only from one major cancer hospital (Maharagama) or selecting controls from a different surgical ward (NHSL).
What is Referral Bias?
Referral Bias is a type of selection bias where cases are selected from a specific location that may not represent the broader population.
Example: Selecting cases only from Maharagama may not represent all breast cancer patients.
What is Berksonian Bias?
Berksonian Bias occurs when hospital-based controls differ systematically from the source population.
Example: Controls from a surgical ward may differ from the general population.
What is Information Bias?
Information Bias occurs when there are inaccuracies in the data collected about exposure or outcome.
Types include Recall Bias and Interviewer Bias.
What is Recall Bias?
Recall Bias is when cases recall past weight or lifestyle factors differently than controls.
Example: Breast cancer patients may remember their past differently than non-cases.
What is Interviewer Bias?
Interviewer Bias occurs when interviewers probe exposure history differently based on their knowledge of case/control status.
This can lead to skewed data collection.
What is Confounding Bias?
Confounding Bias occurs when extraneous factors are associated with both the exposure and outcome, affecting the results.
Examples include age, parity, and lifestyle factors.
Conducting a Cohort Study (on factory workers, e.g., exposure to a chemicaland asthma(33pg epid myanswers))
1.Define Cohorts: Select a group of workers exposed to the factor of interest (e.g., the chemical) and a comparable group of workers not exposed to the factor. Both groups must be free of the outcome (asthma) at the start of the study. 2. Baseline Data: Collect baseline information on exposure levels, potential confounders (e.g. smoking, age, pre-s existing conditions), and confirm absence of the outcome. 3. Follow-up: Follow both the exposed and unexposed cohorts over a specified period (prospectively). The follow-up methods could include periodic health examinations, questionnaires, or checking medical r records. Ensure follow-up SS consistent for both groups. 4. Outcome Ascertainment: Monitor the development of the outcome (asthma) in both groups using standardized diagnostic criteria. 5. Analysis: Compare the incidence of the outcome (asthma) in the exposed group with the incidence in the unexposed group. Measures (Rates) Calculable from a Cohort Study: ◦ Incidence Rate (or Cumulative Incidence) in Exposed Group (le): (Number of new asthma cases in exposed) / (Total person-time at risk in exposed OR Total number initially disease-free in exposed). Iincidence Rate (or Cumulative Incidence) in Unexposed Group (lu): (Number of new asthma cases in unexposed) / (Total person-time at risk in unexposed OR Total number initially disease-free in unexposed). 9 Relative Risk (RR):le /lu. Measures the strength of association between exposure and outcome. Attributable Risk (AR) / Risk Difference: le - lu. Measures the excess risk of the outcome in the exposed group attributable to the exposure,
Atributable Fraction (AF) / Attributable Proportion: (le-lu)/ le * -100%. The proportion of the disease in the exposed group that is attributable to the exposure. Population Attributable Risk (PAR): It (ncidence in total population) jU- Measures the excess risk in the total population attributable to the exposure.
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- Recall Bias
Use blinded, structured questionnaires with neutral language
Keep recal period short whenever possible.
Selection Bias
Use multiple control groups to assess consistency of results
Interviewer/Observer Bias
Blind the interviewer to case/control status.
Use standardized questionnaires
