Epi Info

Epi Info is public domain statistical software for epidemiology developed by Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia (USA).

Epi Info has been in existence for over 20 years and is currently available for Microsoft Windows. The program allows for electronic survey creation, data entry, and analysis. Within the analysis module, analytic routines include t-tests, ANOVA, nonparametric statistics, cross tabulations and stratification with estimates of odds ratios, risk ratios, and risk differences, logistic regression (conditional and unconditional), survival analysis (Kaplan Meier and Cox proportional hazard), and analysis of complex survey data. The software is in the public domain, free, and can be downloaded from http://www.cdc.gov/epiinfo. Limited support is available.

An analysis conducted in 2003 documented over 1,000,000 downloads of Epi Info from 180 countries.

History
Epi Info has been in development for over 20 years. The first version, Epi Info 1, was originally implemented as an MS-DOS batch file on 5.25" floppy disks and released in 1985. MS-DOS continued to be the only supported operating system until the release of Epi Info 2000, which was written in Microsoft's Visual Basic and became the first Windows-compatible version. The last MS-DOS version was Epi Info 6.04d released in January 2001.

Epi Info 2000 changed the way data was stored by adopting the Microsoft Access database format, rather than continuing to use the plain-text file format from the MS-DOS versions. Following the release of Epi Info 2000 was Epi Info 2002, then Epi Info version 3.0, and finally the open-source Epi Info 7. The 7 series is the presently maintained Epi Info product line. Note that Epi Info 3 for Windows is different than Epi Info 3 for MS-DOS even though they share the same version number.

Windows Vista was officially supported with version 3.5.1, released on August 13, 2008.

The next iteration of the Epi Info series, Epi Info 7, was made open source on November 13, 2008 when its source code was uploaded to Codeplex for the first time.

Features
From a user's perspective, one of the most important functions of Epi Info is the ability to rapidly develop a questionnaire, customize the data entry process, quickly enter data into that questionnaire, and then analyze the data. For epidemiological uses, such as outbreak investigations, being able to rapidly create an electronic data entry screen and then do immediate analysis on the collected data can save considerable amounts of time versus using paper surveys.

Epi Info uses three distinct modules to accomplish these tasks: Form Designer, Enter, and Analysis. Other modules include the Report module, a mapping module, a menu module, and various utilities such as StatCalc.

Electronic questionnaires are created in the Form Designer module. Individual questions can be placed anywhere on a page and each form may contain multiple pages. The user is given a high degree of control over the form's appearance and function. The user defines both the question's prompt and the format of the data that is to be collected. Data types include numbers, text strings, dates, times, and Boolean. Users can also create drop-down lists, code tables, and comment legal fields. One of the more powerful features of Form Designer is the ability to program intelligence into a form through a feature called "check code". Check code allows for certain events to occur depending on what action a data entry person has taken. For example, if the data entry person types "Male" into a question on gender, any questions relating to pregnancy might then be hidden or disabled. Skip patterns, message boxes, and math operations are also available. Relational database modeling is supported, as users may link their form to any number of other forms in their database.

The "Classic Analysis" module is where users analyze their data. Import and export functions exist that allow for file types to be converted between plain-text, CSV, Microsoft Excel, Microsoft Access, dBase, FoxPro, and other formats. Many advanced statistical routines are provided, such as t-tests, ANOVA, nonparametric statistics, cross tabulations and stratification with estimates of odds ratios, risk ratios, and risk differences, logistic regression (conditional and unconditional), survival analysis (Kaplan Meier and Cox proportional hazard), and analysis of complex survey data.

The "Visual Dashboard" module is a lighter-weight Analysis component that is designed to be easy to use, but does not contain the full set of data management and statistical commands that the "Classic Analysis" module does.

Using the Map module, data can be displayed either by geographic reference or by GPS coordinates. The Report module (planned) allows the user to edit and format output from various Epi Info tools and modules. The resulting HTML document can then be printed or emailed to others.

The menu module (planned) allows for the editing and re-arranging of the basic Epi Info menu structure. This module is powerful enough that several applications have been built off of it (in versions of Epi Info prior to version 7), including the National Electronic Telecommunications System for Surveillance (NETSS) for Epi Info 6. Unlike the other modules, the menu module does not have a design-mode user interface, but instead resides in a .mnu file whose scripts must be edited manually.

Epi Info 7 also includes a number of nutritional anthropometric functions that can assist in recording and evaluating measurements of length, stature, weight, head circumference, and arm circumference for children and adolescents. They can be used to calculate percentiles and number of standard deviations from the mean (Z-scores) using the CDC/WHO 1978 growth reference, CDC 2000 growth reference, the WHO Child Growth Reference, or the WHO Reference 2007. It replaces the NutStat and EpiNut modules found in prior versions of Epi Info.

Future developments
Version 7 is currently in continuing development as an open-source project and written using Microsoft's C# .NET programming language. Source code distribution and contribution currently takes place through Codeplex. Web-based data entry, reporting capabilities, a fully featured menu module, and handheld/mobile data entry (for Android-based devices) are planned for 2012.