Behavior Science Flashcards
Case control study
Observational, retrospective
Compare a group w disease to a group wo disease n look for exposure or risk factors
What happened
Measures odds ratio
Cross sectional study
Data from a group at a particular point in time
What is happening
Measures Disease prevalence
Establish association not causality between risk factors and disease
Cohort study
Observational, prospective or retrospective
Compares group w exposure to group wo n looks to see if exposure inc likelihood of disease
Who will develop or who did given exposure
Measures relative risk
Four phases of clinical drug trial
Phase 1: small number of healthy, is drug safe, assess toxicity pharmakinetics
Phase 2: small number of patients, does it work, assess treatment efficacy and optimal dosage and side effects
Phase 3: large group randomized w control (placebo or best available), is it good or better, compare w existing treatment
Phase 4: post marketing surveillance, can it stay, long term adverse effects
Sensitivity
Proportion of all people with disease who test positive, or the probability that a test detects disease when disease is present
Value approaching 100% is desirable for ruling out and indicate low false negative rate
Best for screening test
=TP / (TP + FN) = 1 - false negative
SN-N-OUT highly sensitive test when negative rules out disease
Specificity
Proportion of all people without disease who test negative, or the probability that a test indicates non-disease when disease is absent
Value approaching 100% is desirable for ruling in disease and indicates a low-false positive rate
Best for confimrational diagnostic after positive screening
=TN / (TN+FP) = 1 - false positive
SP-P-IN highly specific test, when positive, rules in diseae
Negative predictive value
Proportion of negative test results that are true negative
Probability that person actually is disease free given negative test result
=TN / (TN+FN)
High prevalence or pretest probability = low NPV
Positive predictive value
Proportion of positive test results that are true positive
Probability that person actually has the disease given positive result
=TP/ (TP+FP)
High prevalence or pretest probability = high PPV
Incidence rate
Number of new cases in a specified time period / population at risk during same time period
Looks at new cases
Prevalence
Number of existing cases / population at risk
Looks at all current cases
Odds ratio
Uses in case control studies
Odds that the group with the disease was exposed over the odds that the group w/o the disease was exposed
(a/c)/(b/d) = ad/bc where a and c are small (low prevalence of disease) A is those with disease and exposed C is those with disease and unexposed B is those without disease and exposed D is those without disease and unexposed
Relative risk
Used in cohort studies
Risk of developing disease in exposed group over risk of developing disease in unexposed group
(a/(a+b))/(c/(c+d))
Relative risk reduction
The proportion of risk reduction attributable to intervention as compared to control, RRR= 1-RR
Attributable risk
The difference in risk between exposed and unexposed that is attributable to exposure
AR = a/a+b - c/c+d
Absolute risk reduction
The difference in risk attributable to intervention as compared to a control (raw number percentage)
Numbers need to treat
Number of patients who need to treated for 1 to benefit
=1/ARR
Number needed to harm
Number of patients who need to be exposed to a risk factor to be harmed
=1/AR
Selection bias
Non random assignment to participate in a study group
Study only look at inpatients, studying disease w early mortality but high loss to f/u, studying health workers and volunteers
Can be avoided w randomization
Recall bias
Awareness of disorder alters recall by subjects, common in retrospective studies
Patients w disease recall exposure after learning similar cases
Avoided by decreasing time from exposure to follow u
Measurement bias
Information is gathered in a way that distorts it
Hawthorne effect: groups who know they are being studied behave differently than if they didn’t know
Avoided with placebo control or blinding studies
Procedure bias
Subjects in diff groups are not treated the same
Use sham methods to equalize study groups
Observer bias
Researcher’s belief in efficacy of treatment changes outcome, self fulfilling prophecy
Avoid w double blind studies
Confounding bias
When a factor is related to both exposure and outcome but not the causal pathway
Ex: pulmonary disease, coal mines, smoking
Corrected w crossover studies or matching pts w similar characteristics in study groups
Lead time bias
Early detection is confused w increased survival, often seen w screening techs
Corrected w back end survival measurement, ex: adjust survival according to severity at time of diagnosis
