25 biostats equations - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums 25 biostats equations

 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
04-02-2016
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 369 Threads: 54 Thanked 102 Times in 80 Posts Reputation: 112
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 Guru Steps History: 1+CK+CS+3 Posts: 369 Threads: 54 Thanked 102 Times in 80 Posts Reputation: 112

__________________
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
for
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!!

Last edited by Kruno; 04-07-2016 at 12:12 AM.
#3
07-20-2016
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 369 Threads: 54 Thanked 102 Times in 80 Posts Reputation: 112
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
__________________
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
for
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!!

#4
08-24-2016
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 369 Threads: 54 Thanked 102 Times in 80 Posts Reputation: 112
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

__________________
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
for
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!!
#5
11-03-2016
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 369 Threads: 54 Thanked 102 Times in 80 Posts Reputation: 112
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

__________________
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
for
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!!

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
Favorite USMLE Books
 What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
 Where you live. Leave blank if you don't want to tell.

## Log-in

 Similar Threads Thread Thread Starter Forum Replies Last Post Marķa Zavala USMLE Step 1 Forum 9 05-20-2017 06:52 PM drglo USMLE Step 2 CK Forum 1 06-14-2015 06:12 AM modesty USMLE Step 1 Forum 0 04-26-2012 04:38 AM tunde michael USMLE Step 1 Forum 1 05-27-2010 02:50 PM step1 USMLE Step 1 Forum 4 12-26-2009 11:11 PM