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epidemology Cheat Sheet (DRAFT) by

final review for epi final

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Measures of Morbidity and Mortality

Prevalence: the number of people with the outcome at a specified time; Number of Prevalent cases/ Size of population Incidence: new cases during a time period of interest Incidence Propor­tion: New cases observed during a time period/ People at risk at the start of the time period -at risk meaning you can’t already have the disease Incidence Rate: New cases observed during a time period/ Total Person­-time AT RISK Case Fatality: Number of people who have died from a disease/ Number of people in the population at midyear with the disease Mortality Rate: Number of people who have died from all causes/ Number of people in the population at midyear
 

Measures of Associ­ation

Odds Ratio: Prevalence ratio, preval­ences odd ratio OR = A/B / C/D - Prevalence is snapshot in time Interp­ret­ation: The odd of [disease] was [OR] times as likely in [exposed] compared to [unexp­osed] [over x days/m­ont­hs/­years
Incidence proportion among whole sample: A+C / A+B+C+D Incidence proportion among exposed: A / A+B Incidence proportion among unexposed: C / C+D
Risk Ratio: A/A+B / C/C+D
Ratio Ratio: Incidence rates using person­­-time A/ (person time E+) / C/(person time E-) Interp­­re­t­a­tion: The rate of [disease] was [rate ratio] times as likely in [exposed] compared to [unexp­­osed] over [x] days/ months­­/years
 

Study Designs

Case Report- individual level observ­ations by healthcare providers of what they see during clinical practice
Cross Sectional- slice of time “snapshot” through population capturing exposure and outcome at same time
Case-C­ontrol - Calculates odds of exposure, rather than odds of disease
Cohort Studies- (can be retros­pective or prospe­ctive) 1. Begins w target population 2. Assess the exposure status of sample 3. Follow partic­ipants for some length of time and observe incident cases
Case Series- Case report but focused on more than one patient
Strengths: Cheap, good first step
Strengths: Cheaper than cohort, good for rare disease
Strengths: tempor­ality can be determined prospe­ctively
 
Limita­tion: Temporal Bias, Surviv­al/­Sel­ection Bias, Recall Bias
Limita­tion: Temporal Bias, Surviv­al/­Sel­ection Bias, Recall Bias
Limita­tion: Take a long time, nonpar­tic­ipa­tio­n/n­onr­esponse includes major biases
 
Good for initial invest­igation of associ­ation between a specific exposure and disease
Measure of Associ­ation : Reverse Odds Ratio (A/C)/­(B/D)
Measure of Associ­ation: Risk/Rate Ratio
 
Measure of Associ­ation : Odds Ratio
Interp­ret­ation: The odds of [EXPOSURE] was [OR] times as high in [cases] compared to [controls] over [time period]