Age-Period-Cohort Modeling of Alcohol-Related Hospital Admissions Among Adults 45 and Older

Background and Purpose: Substance use disorders and treatment need among older adults are growing and expected to increase in coming years as members of the baby boom generation and subsequent cohorts enter older adulthood.  The post-World War II generation is unique in its size, and the fact that it experienced emerging adulthood during a period of more permissive attitudes regarding the use of substances, including alcohol.  The period of the 1960’s and 1970’s was distinctive for high prevalence of alcohol and drug use in our nation’s history.  This generation and those following it are reaching old age. Despite the demographic importance of the baby boomer generation and its potential for elevated risk of alcohol use disorders, there has been little research disentangling the effect of age, period and cohort on alcohol related morbidity and consequential acute care hospital use.

This study uses a nationally representative all-payer hospital sample to characterize trends in rates of alcohol related hospitalizations by race and gender and to disentangle the effects of time period, age of individuals, and birth cohort effects. We hypothesized that the increase in rates of alcohol related hospitalizations among older adults observed by other studies would be confirmed, and that baby boomer cohorts would have an elevated risk of hospitalization compared with previous generations.

Methods: Data were analyzed from the Nationwide Inpatient Sample (NIS), an approximately 20% national probability sample of short-stay community hospitals in the United States (6.5 and 8 million discharges per year). Cases of alcohol-related hospitalizations (ARH) were coded using ICD-9 codes from the NIS.  We used the 1993-2010 data to estimate the total number of ARHs, and computed population adjusted rates using census data. We then used linear regressions to analyze trends of ARH rates.  Age, period, cohort analysis (APC) was conducted to understand the effects of these parameters on ARHs.

Results:  Time trends for ARH were notable as they increased over time among those 45-64 years old (b=3.25; t=15.87; p<.001) and 65+ years old (b=.88; t=8.84; p<.001).  Age groups under age 65 demonstrated significantly higher rates of ARH, and age groups over 70 demonstrated significantly lower rates of ARH.  We also found a positive cohort effect for ARH, as individuals in later postwar cohorts showed significantly higher rates of ARH, and those born in prewar and World War II cohorts had significantly lower ARH rates. ARH rates displayed a positive period trend, with the years 1995 and 2000 significantly lower than the mean rate and 2010 significantly greater than the mean rate across years.

Conclusions and Implications: This study adds to evidence that younger cohorts who are aging may have greater morbidity related to alcohol and other substance use, and provides support for the notion that increasing disorder and service use is not simply a function of growing numbers of older adults, but of changes in the rate of ARH diagnosis in this population.  These ballooning rates add to a sense of urgency to prepare the behavioral health workforce to meet the needs of older adults.