Brady Shared "Statistics" - 17 Picmonics

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Statistics

Cohort Study
Observational
Longitudinal
Studies risk from exposure
Retrospective
(Asks) "Who developed disease?"
Prospective
(Asks) "Who will develop disease?"
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1 min
Case Control Study
Observational
Retrospective
Compares those with disease to those without
(Asks) "What happened?"
Measurement
Odds Ratio
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47 secs
Cross-Sectional Study
Observational
(Asks) "What's happening?"
Data at one specific point in time
(Finds) frequency of disease
Measurement
Prevalence
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49 secs
Quantifying Risk: Contingency 2x2 Table Setup
Disease
Along Top (x axis)
Exposure
Along Side (y axis)
A: Exposed and Diseased (Sick)
B: Exposed and Healthy
C: Not Exposed and Diseased (Sick)
D: Not Exposed and Healthy
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2 mins
Sensitivity
Characteristics
Rules Out
Screening Test
Formula
TP / (FN+TP)
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2 mins
Specificity
Characteristics
Rules In
Confirmatory Test
Formula
TN / (TN + FP)
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1 min
Positive Predictive Value (PPV)
Proportion of Positive Tests that are True Positive
Probability that Person with Positive Test has Disease
Formula
TP (True Positives)
Divided by /
All Positive Test Results
TP + FP
Considerations
Varies Directly with Prevalence
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1 min
Negative Predictive Value (NPV)
Proportion of Negative Tests that are Truly Negative
Probability that Person with Negative Test is Healthy
Formula
(TN) True Negatives
Divided by /
All Negative Test Results
(FN + TN)
Considerations
Varies Inversely with Prevalence
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1 min
Odds Ratio (OR)
Use
Case Control Studies
Measures Association Between an Exposure and an Outcome
Formula
Odds of Exposure in Diseased (Sick) Group
a / c
Divided /
Odds of Exposure in Healthy Group
b / d
Interpretation
=1 Exposure does not affect odds
> 1 Exposure increases disease
< 1 Exposure decreases disease
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2 mins
Relative Risk (RR)
Use
Used in Cohort Studies
Formula
Risk of Developing Disease
Equals =
Exposed Group
a / (a + b)
Divided by /
Unexposed Group
c / (c + d)
When Low Prevalence Odds Ratio Approximates Relative Risk
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2 mins
Attributable Risk (AR)
Use
Proportion Exposure Increases Disease
Formula
Incidence of Diseased (Sick)
Equals =
Exposed Group
a / (a + b)
Minus -
Unexposed Group
c / (c + d)
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1 min
Relative Risk Reduction
(risk in unexposed - risk in exposed) / risk in unexposed
Formula
Treatment effects
RRR = 1 - RR
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Absolute risk reduction (ARR)
Effect of Treatment
Formula
Control Event Rate - Experimental Event Rate
NPV - PPV
ARR = (c/(c+d)) - (a/(a+b))
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Attributable Risk Percent (ARP)
Meaning
% of disease caused by exposure
Formula
(Risk in exposed - Risk in unexposed) / Risk in exposed
(Relative Risk - 1) / Relative Risk
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Likelihood Ratio
Meaning
Probablity that person does or doesn't have the disease
Formula
LR+ = Sensitivity / (1- specificity )
LR- = (1- Sensitivity) / Specificity
Interpretation
LR >1
LR = 1
LR < 1
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Likelihood ratio (DELETED)
All Positive Test Results
Sensitivity / (1- Specificity)
All Negative Test Results
(1- sensitivity) / Specificity
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Number needed to treat or harm
Number needed to treat
Number needed to treat
1/ control event rate - experimental event rate
Number needed to harm
Number needed to harm
1 / experimental event rate - control event rate
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