Public Health Flashcards
Study design where the frequency of disease and frequency of risk related factors are assessed in the present.
Cross sectional study - “What is happening”
Disease prevalence but does not assess causality
Study design that compares a group of people with disease to a group of people without disease. Looks to see if odds of prior exposure or risk factor differs by disease state
Case-control study - “what happened”
ODDs ratio
ex) people with COPD had higher odds of a smoking history than those without COPD
Study design that compares a group with a given exposure or risk factor to a group without such exposure. Looks to see if exposure or risk factor is associated with later development of disease.
Cohort study - “Who will develop the disease” or “who developed the disease”
Can be prospective or retrospective
Relative risk
ex) smokers have a higher risk of developing COPD than nonsmokers
Clinical trial phases: phase I
think “SWIM”
Phase I -“is it SAFE”. Small number of healthy volunteers or pt with dz of interest. Assess safety,toxicity, pharmkinetics, pharmdynamics
clinical trial : phase II
think “SWIM”
Phase II- “Does it WORK”. Moderate numbers of patients with disease of interest. Assess treatment efficacy, optimal dosing, and adverse effects
Clinical trial: phase III
think “SWIM”
Phase III- “IMPROVEMENT?” . Large number of pt with placebo and then with treatment. Compares new treatment to current standard of care
Clinical trial: Phase IV
think “SWIM”
Phase IV: “Can it stay in MARKET”. This is after being approved. Detects rare or long term effects
Sensitivity
True positive rate. Probability that when a dz is present then the rest is positive. SCREENING test
If negative then rules OUT a disease. Higher sensitivity has a lower false negative rate.
TP/(TP + FN) = 1- FN rate
Specificity
True negative rate. Probability that when the disease is absent the test is negative. CONFIRMATION test
When positive it rules IN a disease. Higher specificity means lower false positive rate
=TN/(TN+FP) = 1-FP rate
positive predictive value
probability that a person who has a positive test result actually has the disease
PPV= TP/(TP + FP)
varies directly with pretest probability. High pretest probability results in a high PPV
negative predictive value
probability that a negative rest actually does not have the disease
NPV=TN/(TN+FN)
varies indirectly with pretest probability. high pretest probability results in low NPV
Likelihood ratio
Likelihood that a given result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without the target disorder
LR+ >10 and or LR- 0.1 indicates a useful diagnostic test
LR+=sensitivity/(1-specificity)=TP rate/FP rate
LR-=1-sensitivity/specificity= FN rate/TN rate
Odds ratio
Odds of a certain exposure given an event vs the odds of exposure in the absence of that event. Used in case control studies
OR=ad/bc
Relative risk (RR)
the # times risk of cancer in the exposed vs the unexposed. Used in cohort studies
RR=risk in exposure/risk in unexposed
RR=((a/a+b)/(c/c+d))
RR=1 there is not association between exposure and disease
RR>1 there is an association that causes increase in dz
RR<1 there is an association that causes decrease in dz
Attributable risk (AR)
The difference in risk between exposed and unexposed groups
Risk in exposed - risk in unexposed
AR=(a/a+b)-(c/c+d)
Relative risk reduction (RRR)
The proportion in risk reduction attributed to the intervention as compared to a control
RRR=1-RR
Absolute risk reduction (ARR)
The difference in risk (not the proportion) attributable to the intervention as compared to a control
ARR=((c/c+d) - (a/a+b))
Number needed to treat (NNT)
Number needed to treat for 1 patient to benefit
low number is better
NNT=1/ARR
Number needed to harm (NNH)
number needed to be exposed for 1 patient to be harmed
high number is better
NNH=1/AR
Incidence
new cases/#at risk
prevelaence
existing cases/total#of people in a population
increase prevalence causes increase in PPV and decreases in NPV
Precision
reliability
The consistency and reproduciblity of a test. The absence of random variation in a test
Increase precision causes decrease in standard deviation
increase in precision causes increase in statistical power
Accuracy
validity
systemic error decreased accuracy in a test
Berkson bias
study population selected from hospital is less healthy than general population
type of selection bias