# Miriam Shared "MBS" - 11 Picmonics

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### MBS

Cross-Sectional Study
Observational
Data at One Specific Point in Time
(Finds) Frequency of Disease
Measurement
Prevalence
49 secs
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
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
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)
1 min
Case Control Study
Observational
Retrospective
Compares those with disease to those without
Measurement
Odds Ratio
47 secs
Cohort Study
Observational
Longitudinal
Studies risk from exposure
Retrospective
Prospective
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
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
1 min
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
2 mins
Sensitivity
Characteristics
Rules Out
Screening Test
Formula
TP / (FN+TP)
2 mins
Specificity
Characteristics
Rules In
Confirmatory Test
Formula
TN / (TN + FP)
1 min