# Epidemiology

## Epidemiology is the study of disease states in populations

Epidemiology is the study of disease states at the population level. Epidemiological calculations serve as the

In the applied sense, the

**bridge**between the**utility**of clinical evidence and the**diagnostic and treatment decisions**made in the clinical environment. The results of randomized controlled trials of clinical interventions and some types of observational evidence are used to understand how treatments cause either efficacious or detrimental effects in human populations. Epidemiology further allows researchers to understand the etiological, societal, geographical, and personal aspects of disease states.In the applied sense, the

**2x2 table**does a lot of "heavy lifting" in epidemiology. The 2x2 table is used to calculate epidemiological measures like**odds ratios**,**prevalence**,**relative risk**,**incidence**,**control event rate**,**experimental event rate**,**absolute risk reduction**,**absolute risk increase**,**number needed to treat**, and**number needed to harm**.**The 2x2 table**

Just like with all other parts of conducting a research study, the specific type of epidemiological measure is chosen to

**answer the epidemiological question**. Click on a button below to continue.### Calculations used in epidemiology

The

**u****nadjusted odds ratio with 95% confidence interval**is a measure of**association**between categorical predictor and categorical outcome variables in**retrospective case-control**designs.**Adjusted odds ratios with 95% confidence intervals**are often reported in the medical literature as the**primary inference yielded from logistic regression analyses**.**Prevalence**is the

**number of current cases**that exist in a given population at any time.

**Relative risk**

**(RR)**is the measure of

**association**between categorical predictor and categorical outcome variables in retrospective cohort, prospective cohort, RCT, and epidemiological designs.

**Incidence**is the

**number of new cases**in a given population moving forward in time.

The

**control event rate (CER)**is the**proportion****of individuals in the control group of an RCT that have the outcome**.The

**experimental event rate**(EER) is the**proportion of individuals in the treatment group of an RCT that have the outcome.**The

**treatment effect**is related to the outcome of the treatment being efficacious (reducing bad outcomes) or detrimental (increasing bad outcomes).Given the treatment is thought to be

**efficacious**,**absolute risk reduction (ARR)**is the**absolute difference**between the**CER**and**EER**.**|CER - EER|****Number needed to treat (NNT)**is the

**number of people that need to be treated to prevent one bad outcome in the future**.

**(1/ARR)**

Given the treatment could be potentially

**detrimental**,**absolute risk increase (ARI)**is the**absolute difference**between the**CER**and**EER**.**|CER - EER|****Number needed to harm (NNH)**is the

**number of people that need to be treated to cause a bad outcome in the future**.

**(1/ARI)**

### Downloads for epidemiology

Click on the

**Download Database**for**a free Excel database formatted for epidemiology data.**Click on the

**Download Calculator**for a free Excel calculator for epidemiology calculations.## Hire A Statistician - Statistical Consulting for Professionals

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- Statistical Analysis
- Research Design
- Sample Size Calculations
- Diagnostic Testing and Epidemiological Calculations
- Survey Design and Psychometrics