Public Health Sciences Flashcards
(123 cards)
Cross sectional study
Frequency of disease and risk factors both assessed in the present
Measured by disease prevalence
Case control study
Group of people with a disease compared to a group without disease, look at ODDS of prior exposure or risk factor makes a difference
Measured by OR
Cohort study
Looks at a group with a given exposure/risk and a group without and assesses risk factor association with disease development later on
Measured by RR
Can be prospective (who will develop) or retrospective (who developed)
Phase I drug trials
Assesses safety, toxicity, pharmacokinetics/dynamics in small # of healthy volunteers
Phase II drug trials
Assesses if it works – treatment efficacy, optimal dosing, adverse effects in small # pts with disease
Phase III drug trials
Compares tx to standard of care or placebo to see if its an improvement in a large number of randomly assigned patients with disease
Phase IV drug trials
Postmarketing surveillance – if rare/long-term adverse effects may be withdrawn from market
Sensitivity
TP/(TP+FN) or 1-FN
Def: when disease present, how many test positive
Highly sensitive rules OUT disease (i.e. low false negative) – best for screening
Specificity
TN/(FP+TN) or 1-FP
Def: when disease not present, how many test negative
Highly specific rules IN disease (i.e. low false positive) – best for confirmation after screening
PPV
TP/(TP+FP)
Def: Proportion of positives that are true positives
Person with a positive test actually has disease
Varies with pretest probability (higher pretest prob –> higher PPV)
NPV
TN/(TN+FN)
Def: Proportion of negatives that are true negatives
Person with a negative actually doesn’t have disease
Varies w/ pretest probability (higher pretest prob –> lower NPV)
LR+
Sense/(1-spec) = TP/FP
>10 useful diagnostic test
LR-
(1-sens)/spec = TN/FN
<0.1 useful diagnostic test
(- –> negative sign on top!)
Odds ratio
OR=(a/b)/(c/d) or ad/bc
Used in case control studies to depict odd of event given an exposure vs odds of it happening w/o exposure
Relative risk
=[a/(a+b)]/[c/(c+d)]
Used in cohort studies to determine risk of developing disease in exposure group divided by risk in unexposed group
-For rare disease (i.e. low prevalence) – approximates RR
-If 1 –> no relationship between exposure/disease
-If >1 –> positive association between disease and exposure
-If <1 –> negative association between disease and exposure
Attributable risk
Difference in risk between exposed and unexposed groups – proportion of disease attributable to exposure
AR=[a/(a+b)]-[c/(c+d)]
Relative risk reduction
Proportion of risk reduction attributable to an intervention vs control
RRR=1-RR
Absolute risk reduction
Difference in risk (not proportion) attributable to intervention vs control
ARR = [c/(c+d)]-[a/(a+b)]
ABCD on table!
disease
+ -
risk factor + a b
- c d
NNT
Number needed to be treated for 1 pt to benefit (lower is better)
=1/ARR
NNH
Number needed to be exposed to risk factor for 1 patient to be harmed (higher number is better)
=1/AR
Precision
aka reliability Reproducibility – increased=lower SD, higher statistical power
Accuracy
aka validity Trueness of test measurements – absence of systematic error/bias in a test
Selection bias
Non random sampling or treatment allocation so that population in study is not representative (usually a sampling bias
