Most jails operate two distinct functions: a short-term lockup where inmates are temporarily detained before they are released, and a longer-term detention and corrections facility. Although national statistics are not available, it is likely that the average jail releases more than 75% of its inmates within 72 hours.

The short-term pre-arraignment detainees who comprise the vast majority of the inmates who enter our jails, account for a very small proportion of the jail beds on a given day. It is not unusual to find that these 72-hour-or-less inmates occupy under 5% of the beds.

This dynamic—lots of short-term detainees (measured in hours) dominating the admissions but occupying very few beds—often results in serious misconceptions about the jail population by the public. When we talk about “average length of stay“ for a jail inmate, we are describing the jail population based on admissions but we are seriousness of the inmate population.

While analyzing inmate length of stay may be an important tool for managers and policymakers, it should always be tempered by an understanding of the dynamics of the jail. In many jurisdictions, this is accomplished by describing inmate population dynamics in terms of both admissions and detention days (number of days spent.)

The following chart is an good example of the way the admissions, detention days, and length of stay may be combined to provide a three-dimension view of the dynamics of the jail population.

XXX County officials should be proactive in their efforts to manage, and hopefully decrease, the rate of growth of future jail populations.  Finding effective points of intervention requires a further review of the data.

As the previous chapters of this report suggest, the dramatic increase in the jail population growth can be attributed in part to the length of stay for jail inmates.  Figure 1 underscores the impact of inmate length of stay in the past three years.

As the chart demonstrates, admissions to the XXX County Jail increased by less than 1 percent in the past three years, while the number of inmate detention days increased by nearly 28 percent.  The length of stay for inmates clearly is responsible for the increase.

As we reported earlier, nearly half of the inmates admitted to the XXX County Jail spend less than one day in confinement, but most of the jail beds are used by inmates who spend 30 or more days in confinement.  This is depicted in Figure 2.

FIGURE 2
Admissions v. Detention Days (4 Year Dataset)

Figure 3 shows that 76.1 percent of all inmates are released within three days, but they account for only 3.0 percent of the jail beds.  Conversely, 3.4 percent of the inmates spend more than 90 days in jail, but they account for 47.9 percent of the jail beds.

FIGURE 3
Cumulative Percentage of Admissions v. Detention Days 

 Figure 4 provides a graphic portrayal of how the length of stay drops off in the first hours after admission to the jail.

FIGURE 4
Percent of Inmates Remaining In Jail by Days

Figure 5 provides another view of length of stay, depicting the small proportion of beds that are used by the inmates who are confined for short periods of time.

FIGURE 5
Percent of Beds Used by Inmate Length of Stay

Inmates who spend less than 11 days in confinement account for only 5.*% of the beds used, but represent 82.7 percent of the admissions. Figure 6 provides a breakdown of the very short-term inmates for the calendar year 2004.

FIGURE 6
Length of Stay by Hours (3 days and Less), Calendar Year 2004

Figure 6 shows that 61.5 percent of all inmates admitted in 2004 were released from jail within 72 hours of admission, and 33.3 percent were released within 24 hours.  This analysis is useful during the planning and design process, as it provides insights into the need for short-term detention.  In particular, it is relevant to planning an expanded or new intake and booking area, which would resemble a large processing center that could hold and manage new admissions for up to eight hours and facilitate releases, if appropriate, prior to being placed in a jail cell.

A further examination of the length of stay by year helps to focus on the specific areas of growth.  Figure 7 shows the changes in length of stay in the past four years.

FIGURE 7
Percent of Detention Days by Length of Stay, 7/2000 – 6/2004

While the number of beds occupied by inmates who spent over 180 days dropped substantially after 2000-01, the beds used by inmates who spent between 31 and 120 days in confinement increased by 93.3 percent.