We appreciate Milani’s question regarding the definition of frequent emergency department (ED) visits in our article. According to several articles cited by Milani, along with the studies cited by these articles, thresholds range from as few as two to 12 or more visits per year. Although many studies use four or more ED visits to define frequent ED use for the general population, there is currently no commonly agreed upon definition as noted in these articles and literature. The threshold depends on the purpose of the study, the distribution of data, and the consideration of policy implications. Homeless individuals experience much higher health care utilization than the general population.4,5 The average number of ED visits in our study reached four visits per year and a group of individuals showed high ED use. Therefore, we classified homeless individuals into four groups (0, 1–2, 3–5, and ≥ 6 ED visits). These four groups were significantly different, which is consistent with existing literature.
Furthermore, the patterns of incremental changes in population characteristics along with increased ED use did not present an obvious single threshold to separate the study population. Instead of simply dichotomizing the study population, we modeled the number of ED visits as count data to avoid losing important information, particularly for extremely high users. Results were presented in incidence rate ratios, which represent the ratio of the count of ED visits for the variable of interest to its reference group. For example, the number of ED visits for individuals with co-occurring schizophrenia and substance use disorders was almost eight times higher than for those without behavioral health disorders. In other words, the former group experienced much more frequent ED visits than the latter group when other variables were held equal.
The high health care utilization for homeless individuals prompted us to examine the number of events rather than relying on the conventional dichotomous group approach. Along with the descriptive analysis for groups with various levels of ED use, the study provides useful information to assist the planning of interventions.
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