Variable Computations

Each participating institution is provided with their raw data, which also includes computations of Body Mass Index (BMI), estimated Blood Alcohol Concentration (BAC), and a screened variable for depression diagnosis and treatment. Results are presented in an Institutional Report that presents frequency distributions for each variable across all subjects and by gender. In addition, participants are offered an Institutional Executive Summary developed by the NCHA Advisory Committee to highlight salient issues. A Reference Group Report and Reference Group Executive Summary are produced each semester and contain the aggregated data from all participating institutions.

Computations of Body Mass Index (BMI)

BMI is computed as weight in kilograms (kg) divided by the square of height in meters (m2).

BMI = weight[kg]/height[m2]

A BMI and the corresponding Healthy People 2010 category (ranging from underweight to class III obesity) are provided for each subject.

Estimated Blood Alcohol Concentration (BAC)

Estimated BAC is computed using a formula provided by the U.S. Department of Transportation, National Highway Traffic Safety Administration. The formula is applied to the reported number of drinks and number of hours for the last time students "partied"/socialized, weight, as well as estimates for total body water weight (58% for males and 49% for females) and the average rate of alcohol metabolism (a decline of .017 per hour). The formula does not control for food consumption and assumes that the alcohol was consumed at a constant rate over the drinking episode.


The variable “Ever Diagnosed with Depression” has an instruction on the survey, that directs if “no” please go to question 42 (skip the next three questions). Some respondents indicated “no” to “Ever Diagnosed with Depression” and then answered the next three questions regarding current diagnosis and treatment. Because of this, three variables are formed for each Institutional Database and the Reference Group Databases based on a screen (criteria) that allows only participants that indicated “yes” to “Ever Diagnosed with Depression” to respond to current diagnosis and treatment questions. This screen is used in the Institutional Executive Summaries and the Reference Group Executive Summaries.