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Flashcards in Case controlled studies Deck (15)
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What are the main criteria for assessing caussation

Bradford-Hill criteria:
Strength of association (relative risk, odds raito), consistency, specificity (single), temporality, dose responsse relationship, biological plausibility
coherence, exxperimental evidence, analogy


why are reports of association between genotypes and outcome so inconnsistent

variation of underlying asssociation between genotype and outcome between populations
heterogenous phenotypes
confounding by population stratification
failure to exclude chance as explaanaation
publication bias


What are the advantages+disadvantages of case control studies

Advantages: Inexpensive and quick
Good for rare outcomes and multiple risk factors
Can look at risk factors in detail
Disadvantage: not good for rare exposures, prone to selection, recall bias, uncertainty of exposure-disease time relaitonship, inability to provide direct estimate of risk, not efficient for studying rare exposures


what are the features of a case control study

retrospective, obtained from past/information that is lifelong
no follow up=quick aanswer
suitable for rare diseases-all accessible cases can be located and controls found afterwards


What does the odds ratio do

estimates ratio of disease odds in exposedd group to disease odds in unexpossed group in study population


how to work out odds of event happening in exposed group and unexposed

exposed: pe/1-pe


If there is no association existing between exposure and disease stauts

Odds ratio should bee equal a/b=c/d


How to calculate odds ratio



What does it mean if odds ratio is greater than 1 and less than 1

greater=increase in risk
less=protective or reduced risk


What does it mean if 95% CI contains 1 or Odds ratio=1

95% contain 1: little evidence against null hypothesis
Odds ratio=1: no difference beetween exposed and non exposed population


What does 95% CI mean

95% of the time confident that the interval includes true population parameter


What does P value=0.05 mean

1/20 likelihood that something is occuring by chance


What are the main types of bias

selection bias (case/control/exposure/sampling/response), information bias (misclassification of source and type), confounding, admission bias (higher chance of admisssion doesn't equate to prevalence of disease), diagnostic bias (more likely to check up if knowledge of certain activities), survival bias (only survivers can enter study), non response bias (people who can't be contacted may have higher/lower OR), recall bias, interviewer bias


What is confounding

situation wheere association between exposure and outcome is entirely/partially due to another exposure


what are the pros and cons for cohort study

pro: exposure measured before disease onset, allows multiple outcomes per exposure including incidence, rare exposure by selection, offer advantages less recall bias
cons: insufficient for rare diseases, prospective (expensive and time consuming\, retrospective (inadequate redcords), validity can be affected by loss to follow up