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#1
04-02-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95
25 biostats equations

not all of these equations are important for the usmle, but its helpful to learn a few. and if you know a little biostats and can visualize a two by two sample table, then you can probably figure out most of them.

Sensitivity = A / (A+C)
False Negative Rate = C / (A+C)
Specificity = D / (B+D)
False Positive Rate = B / (B+D)

Positive Predictive Value = A / (A+B)
False Discovery Rate = B / (B+D)
Negative Predictive Value = D / (C+D)
False Omission Rate = C / (C+D)

Positive Likelihood Ratio = [A / (A+C)] / [B / (B+D)]
Negative Likelihood Ratio = [C / (A+C)] / [D / (B+D)]
Informedness = [A / (A+C)] + [D / (B+D)] - 1
Markedness = [A / (A+B)] + [D / (C+D)] - 1

Accuracy = (A+D) / (A+B+C+D)
Precision = A / (A+B)

Relative Risk = [A / (A+B)] / [C / (C+D)]
Relative Risk Reduction = 1 - [A / (A+B)] / [C / (C+D)]
Absolute Risk Reduction = [C / (C+D)] - [A / (A+B)]
Number Needed To Treat = 1 / [C / (C+D)] - [A / (A+B)]
Attributable Risk = [A / (A+B)] - [C / (C+D)]
Number Needed To Harm = 1 / [A / (A+B)] - [C / (C+D)]

Odds of Exposure (Cases) = A / C
Odds of Exposure (Controls) = B / D
Odds Ratio = (A / C) / (B / D)

Prevalence = [(A+C) / (A+B+C+D)]
Incidence = [(A+C) / (A+B+C+D)] / Time Period

don't try to memorize these equations... the list is here to help illustrate the pattern. i tried to organize these equations in a way that's easy to follow, but if you would like a better visual presentation, check out my youtube video... List of Equations

Last edited by Kruno; 04-07-2016 at 12:22 AM.

#2
04-03-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95

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Last edited by Kruno; 04-07-2016 at 12:12 AM.
#3
07-20-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95
Definitions and Equations

Definitions and Equations

Here is the same list, but with a youtube link for each equation. These short videos show the definition and briefly explain how to make the calculation.

Sensitivity = A / (A+C)
False Negative Rate = C / (A+C)
Specificity = D / (B+D)
False Positive Rate = B / (B+D)

Positive Predictive Value = A / (A+B)
False Discovery Rate = B / (B+D)
Negative Predictive Value = D / (C+D)
False Omission Rate = C / (C+D)

Positive Likelihood Ratio = [A / (A+C)] / [B / (B+D)]
Negative Likelihood Ratio = [C / (A+C)] / [D / (B+D)]
Informedness = [A / (A+C)] + [D / (B+D)] - 1
Markedness = [A / (A+B)] + [D / (C+D)] - 1

Accuracy = (A+D) / (A+B+C+D)
Precision = A / (A+B)

Relative Risk = [A / (A+B)] / [C / (C+D)]
Relative Risk Reduction = 1 - [A / (A+B)] / [C / (C+D)]
Absolute Risk Reduction = [C / (C+D)] - [A / (A+B)]
Number Needed To Treat = 1 / [C / (C+D)] - [A / (A+B)]
Attributable Risk = [A / (A+B)] - [C / (C+D)]
Number Needed To Harm = 1 / [A / (A+B)] - [C / (C+D)]

Odds of Exposure (Cases) = A / C
Odds of Exposure (Controls) = B / D
Odds Ratio = (A / C) / (B / D)

Prevalence = [(A+C) / (A+B+C+D)]
Incidence = [(A+C) / (A+B+C+D)] / Time Period
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#4
08-24-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95
step-by-step

here is new playlist of quick calculations for the 25 biostats equations in my EpiStats channel. the videos use a biostats calculator (which has a sample table) to show each step that is required to make the calculation.

Absolute Risk Reduction

Accuracy

Attributable Risk

False Discovery Rate

False Negative Rate

False Omission Rate

False Positive Rate

Informedness

Incidence

Markedness

Negative Likelihood Ratio

Number Needed To Harm

Number Needed To Treat

Negative Predictive Value

Odds of Exposure (Cases)

Odds of Exposure (Controls)

Odds Ratio

Positive Likelihood Ratio

Positive Predictive Value

Precision

Prevalence

Relative Risk

Relative Risk Reduction

Sensitivity

Specificity

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#5
11-03-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95
equations

i have almost completed a playlist of animated lectures which demonstrate how to make each calculation, but in the meantime.... here is the equations table from the quick info section of the EpiStats app

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