Health of the Force


Last Updated: April 23, 2019

Methods Summary for 2018 Health of the Force

Health Metrics

Data for many of the health metrics presented in the Health of the Force came from administrative medical records in the Defense Medical Surveillance System (DMSS) (i.e., injury, behavioral health, substance use, sleep disorders, and chronic disease).  Obesity data were furnished from outpatient medical encounters by the Patient Administration Systems and Biostatistics Activity.  Tobacco use data were obtained from the Periodic Health Assessment (PHA) survey.  Heat illness data came from the Disease Reporting System, internet (DRSi) and the Military Health System Management Analysis and Reporting Tool (M2).  Sexually transmitted infection data came from the DRSi.  Hearing data were assessed from Defense Occupational and Environmental Health Readiness System – Hearing Conservation (DOEHRS-HC). 

Installation assignment was determined by the Soldier's unit ZIP code at the time of the medical encounter for incidence measures or location at the end of the year for prevalence measures. International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes were used to group individual diagnoses into major health outcomes of interest:  injury, behavioral health, sleep disorders, obesity, tobacco use, heat illnesses, hearing, sexually transmitted infection and chronic diseases.  Specific conditions of interest are reported, in addition to categorical outcomes (e.g., arthritis is reported as a specific condition of interest under chronic disease).

Person-years were calculated by summing the amount of time that Soldiers were at each installation. Crude incidence rates were calculated for injuries and sexually transmitted infections by summing the number of Soldiers with that condition by demographic group (i.e., installation, sex, and age) and dividing it by the sum of the person-years.  Army-wide incidence per 1,000 person-years was also calculated.  Crude prevalence rates were calculated for the remaining health metrics by dividing the number of people with the condition in a demographic group by the total number of people at the same installation.

The 2015 Army Active Component (AC) population was used as the reference population for age and sex adjustments.

Environmental Health Indicators

Air quality data representing installations within the U.S. were obtained from the Air Quality Index (AQI) Reports and Daily Data Summaries published by the U.S. Environmental Protection Agency (EPA).  Data for installations outside the U.S. were obtained from host nation environmental data repositories.  Daily pollutant concentrations were converted to the EPA AQI.  Days with AQI greater than 100 were summed to determine the total number of poor air quality days experienced at an installation in 2017.

Water quality status was evaluated by the presence and type of Safe Drinking Water Act (SDWA) violations that occurred in 2017.  Annual average fluoride level in installation drinking water was evaluated and compared to the U.S. Centers for Disease Control and Prevention (CDC) recommended target concentration and SDWA thresholds.  Solid waste diversion was calculated as the percent of non-hazardous solid waste diverted from disposal, and compared to the target Department of Defense (DOD) Measure of Merit.

Mosquito-borne disease and tick-borne disease risk indices were calculated using mosquito surveillance at Army installations, and the DOD Human Tick Test Kit Program data, respectively.  Surveillance mosquitoes were tested for presence of pathogens including Zika, dengue, chikungunya and West Nile viruses, while the ticks were tested for presence of Lyme disease.

Performance Triad

Sleep, activity, and nutrition (SAN) are the three pillars of the Performance Triad (P3).  The reporting of each SAN domain was revised in 2018 to reflect the percentage of Soldiers meeting national SAN guidelines (e.g., CDC, National Sleep Foundation (NSF)).  The revised reporting method allowed for interpretation of SAN metrics in terms of these standards, leading to an enhanced ability to compare with other groups; and facilitating actionable changes that target areas for improvement.  Estimates were derived from relevant survey items collected within the Global Assessment Tool (GAT), which Soldiers are required to complete annually. 

Installation Health Index (IHI)

In generating an IHI, the eight selected metrics (injury, behavioral health, obesity, sleep disorders, chronic disease, tobacco use, chlamydia, and air quality) were individually standardized to the Army average using Z-scores.  These scores reflect the installation's number of standard deviations (amount of variation in data values for a given metric) from the Army average.  Metric values above the Army average have positive Z-scores, while values below the Army average have negative Z-scores.  Estimates found to be 2 or more standard deviations above or below the Army average are typically considered to reflect statistically significant deviations with a 95% confidence level (95% level of confidence that the true value lies in this interval).

With the exception of air quality data, metrics were adjusted by age and sex prior to standardization to allow more valid comparisons.  Z-scores were then weighted to prioritize readiness detractors (injury 20%, behavioral health 15%, sleep disorders 15%, obesity 15%, chronic disease 15%, tobacco use 10%, chlamydia 5%, and air quality 5%). 

IHI scores were converted to percentiles for ease of interpretation.  Higher percentiles reflect more favorable health status.  The computed percentiles were adjusted to reflect percentages from the maximum observed value or best ranking installation.  For example, if the highest observed percentile for a given metric or IHI was 87%, that installation was considered to be at 100%, and all other installation percentiles were computed relative to this maximum achievable value.