This section provides an estimate of the number of inmates needed by Johnson County over the next ten years, and the number of jail beds needed to support the County's projected inmate population.

Four sets of inmate population projections were developed for planning purposes, using four different forecasting models.

l Model #1 was based on the County's jail population trends over the past 19 years (i.e., 1981 - 1999). This model assumes that the jail population is going to continue to grow for the next 20 years at the same rate it has increased over the past 19 years.

l Model #2 was based on the County's jail population trends over the past 7 years (i.e., 1993 - 1999). This model assumes that the jail population is going to continue to grow for the next 20 years at the same rate it has increased over the past 7 years.

l Model #3 was based on the historical correlation between the growth of the jail population and the growth of the County's total population over the past 20 years, as applied to the population projections for the County over the next 20 years. This model assumes that the jail population is going to continue to grow for the next 20 years in correlation with the projected growth of the County's total population.

l Model #4 was based on the historical correlation between the growth of the jail population and the growth of the County's population between the ages of 18 and 64 over the past 20 years, as applied to the population projections for that age group in the County over the next 20 years. This model assumes that the jail population is going to continue to grow for the next 20 years in correlation with the projected growth of the County's 18 to 64 year old population.

The results of Models #3 and #4 (the population correlation models) both closely tracked with the results of Model #1 (the 1981 - 1999 jail population trend), which was used to establish the low parameter of the projection range. The results of Model #2 (the 1993 - 1999 jail population trend) were used to establish the high parameter of the projection range.

The midpoint of Models #1 and #2 was used as the baseline ADP forecast for planning purposes. According to this baseline forecast, it is estimated that Johnson County will have an average daily population of:

l 111 inmates within five years (i.e., by 2004);

l 136 inmates within ten years (i.e., by 2009);

l 161 inmates within 15 years (i.e., by 2014); and

l 185 inmates within 20 years (i.e., by 2019).

The graph and table on page 20 show the actual ADP and the baseline ADP forecast, as well as the high and low projection parameters.

Obviously, inmate population projections are not an exact science. There are a multitude of ever-changing variables, both tangible and intangible, that can directly impact the size of Johnson County's jail population. Changes in criminal penalties, law enforcement practices, sentencing policies, and crime rates will all have a direct impact on the County's future jail population and its need for additional jail beds.

In addition, it should be noted the further out the projection in made, the less reliable the estimate becomes. Nonetheless, it is believed that the inmate population projections presented here provide reasonable planning goals for the County.

To determine the total number of jail beds needed by Johnson County, two factors were then applied to the baseline ADP projections.

A peaking factor was applied to the baseline forecast to accommodate routine fluctuations above the ADP. To determine an appropriate peaking factor, an analysis was made of the average percentage that the high inmate population exceeded the ADP from January of 1993 through October of 1999. During this period, the peak population averaged 25.2 percent over the ADP each month. Therefore, a peaking factor of 25 percent was added to the baseline ADP forecast.

A classification factor was then applied in order to ensure sufficient jail capacity for inmate classification and management purposes. A conservative classification factor of 10 percent was used to provide sufficient capacity to allow for the separation of males from females, to separate inmates by security classification, and to allow further segregation for administrative, disciplinary, and protective custody purposes.

By applying these two factors to the baseline ADP forecast, the total number of jail beds needed by Johnson County was calculated. The results of these calculations are shown in the following table.

Using this methodology, it is estimated that Johnson County will need a total of:

l 153 jail beds within five years (i.e., by 2004);

l 187 jail beds within ten years (i.e., by 2009);

l 221 jail beds within 15 years (i.e., by 2014); and

l 255 jail beds within 20 years (i.e., by 2019).

Year	1981 - 1999 Trend	Midpoint (Baseline)	1993 - 1999 Trend
2004	99.5	111.4	123.4
2009	116.0	136.1	156.2
2014	132.4	160.7	189.0
2019	148.9	185.4	221.8

III. Johnson County Jail