Demographic Forecast


“Standing against this assertion of the absolute impossibility of knowing the future is the absolute necessity of a picture of the future if behavior is to have any sense.”

– Nathan Keyfitz. 1987. The social and political context of population forecasting. In The Politics of Numbers, edited by William Alonso and Paul Starr. New York: Russell Sage Foundation.

Why Forecast?

Population Forecasts are central to the development of a future plan. The comprehensive plan of a community is a vision for its future. Forecasts attempt to quantify the future and therefore help in formulating the vision. They also provide a basis for quantifying the amount of land that should be allocated to different uses so that the plan accommodates the future needs of the community.

The Two Growth Scenarios

This section presents detailed population and employment forecasts of the future of Pittsfield. It is impossible to accurately predict the future but it is possible to get a sense of what the future of Pittsfield might be like based on information and analysis of the past and the present trends. Two scenarios are portrayed to delineate possible outcomes in the year 2015 (Figure 2.5).  These scenarios do not include persons housed in group quarters, this includes the inmates at the work camp and persons in institutionalized settings like nursing homes.

Graph Showing City of Pittsfield - The Two Growth Scenarios
  1. The first scenario is the ‘slow growth’ scenario that projects a 2015 population of about 4,490 people an increase of only 256 people in 16 years. This scenario assumes that economic growth in Pittsfield will reverse the trend of a marginal population decline but will not be adequate to substantially increase population growth.
  2. The second scenario is the ‘moderate growth’ scenario that projects a 2015 population of about 4,860 people, an increase of about 626 people in 16 years. This scenario assumes that Pittsfield will be able to stimulate and sustain economic growth creating over 600 new jobs by 2015.

Rationale for Scenario 1

This scenario assumes that very little will change in the next 15 years and that Pittsfield is not very successful in attracting in-migrants by significantly stimulating economic development or by enhancing its unique small town character. Historically Pittsfield has shown no substantial increase in population in the last 25 years. In the five decades since 1960 the population of Pittsfield has fluctuated by only a few a hundred people, its population remaining between about 4,100 and 4,300 people. In addition the population of Pike County has declined by over 2,000 in the last thirty years. However the trend of employment growth in Pike County in the last 10 years will tend to discourage the out-migration of its residents and may attract some in-migrants (refer to the section on Pittsfield’s Economy).

Pittsfield is the largest city in Pike County, accounting for a fourth of the County’s population. It has quality schools that also serve other smaller towns within Pike County. It therefore seems very likely that the City of Pittsfield will attract most of the in-migrants into Pike County. Hence assuming that the trend of employment growth in Pike County continues, a prediction of a small increase in Pittsfield’s population is reasonable. Figure 2.6 shows the comparison of population distributions between the years 2015 and 1990 by five-year age groups. An increase is estimated in the ages from 50 to 64, while a decline is predicted in the 30 to 44 age group. Besides the effects of migration, which is relatively small in this scenario the increase in the age group 50 to 64 in 2015 is largely due to the aging of 30 to 44 year old population.

Rationale for Scenario 2

Pittsfield has had a relatively stagnant population in the past 10 years while Pike County as a whole has declined in population over 25 years. In the light of these two facts the second scenario of ‘moderate growth’ seems optimistic. Yet even after losing over 1,500 jobs in the twenty years since 1969, Pike County made a remarkable recovery by gaining 1,665 jobs in the ten years since 1988. Pittsfield, the seat of Pike County, accounts for almost a fourth of the County’s economy in terms of employment. Hence in the absence of detailed employment data for Pittsfield there is an argument for predicting growth in Pittsfield if Pike County continues to sustain the employment growth that it has exhibited in the past 12 years. In addition, it is also important to keep in perspective that Pittsfield is actively planning for tomorrow – economic development is a core aspect of the plan.  With a comprehensive plan, Pittsfield can market itself as a town that has a vision for the future of its community thus attracting businesses and industries. If Pittsfield is successful in attracting businesses and industries – its gain in employment opportunities will encourage people to come into Pittsfield while reducing out-migration of its residents. Here again figure 2.7 shows that the year 2015 population based on scenario 2 has an increase in the population of the 50 to 64 aged cohorts due to the aging of the people in the 30 to 44 cohorts in the year 1990. However, the effect of migration is stronger in this scenario and hence we have more significant increases in other age cohorts.

Forecast Details

As mentioned earlier a significant purpose of the forecasts is to get a reasonable estimate of the amount of land that needs to be allocated for the future growth of Pittsfield. Hence, the land use plan for Pittsfield will be based on the land area calculated from the forecasts of population and employment. Since Scenario 2 will have a greater impact on the physical form of the city in terms of growth and development than the slow growth scenario in this section, the moderate growth forecast will be considered in greater detail. The logic for this is that if the plan accommodates the scenario with more growth it would have also accommodated for the slower growth scenario.

Projection Technique

Population and employment trend data for rural communities is provided on a limited basis by the Bureau of the Census. The only dependable series information is published as a part of the decennial census. Information on migration and birth/death rates that are essential in modeling population growth are not available. The smallest geographic unit for which detailed time series data for population and employment and other detailed demographic information is available is a county. Since projections rely heavily on past data available in time series we developed detailed forecasts for Pike County using all the available data and then extrapolated the projections of Pittsfield as a share of Pike County.

The population of Pike County was estimated based on the cohort component model that uses the migration rates, birth and death rates of five-year age cohorts (a breakdown of the population into 5 year age groups) to arrive at future projections in five-year increments (as the migration data available from the U.S. census is in five year time periods). This technique requires assumptions about in and out migration rates in the future based on the 1985-1990 migration data (the most recent migration data available). The 1985-1990 migration rates are adjusted to ensure that the known population totals of the years 1995 and 2000 are reached before forecasting into the future.

  • In the ‘slow growth’ scenario it was assumed that Pike County’s in-migration rate between 2000-2015 would be 1.2 times the in-migration rate of the 1985-1990 period and the out-migration rate between 2000-2015 would be 0.8 times the out-migration rate of the 1985-1990 period.
  • In the ‘moderate growth’ scenario it was assumed that Pike County’s in-migration rate between 2000-2015 would be 1.38 times the in-migration rate of the 1985-1990 period and the out-migration rate between 2000-2015 would be 0.77 times the out-migration rate of the 1985-1990 period.

To back up these assumptions and the cohort component method, an employment driven population model was also used that was based on the analysis of the past trends of employment (from 1969 to 1998) in Pike County by each 2 digit SIC sector. A bottom-up approach was used where employment in each broad industrial sector (such as wholesale trade, retail trade, services, government etc) was projected and then added together to reach the forecasts of total employment in 2010 and 2015. The employment driven population for 2010 and 2015 was then calculated by multiplying the projected total employment and the projected population employment ratios for 2010 and 2015. This method also requires that assumptions be made about the future rate of employment growth and the rate of change of the population employment ratio.

Projected Land Requirements by 2015

  1. Projected population increase by 2015 = 626 people
  2. Average number of people per household in Pittsfield = 2.22 (based on the 2000 Census)
  3. Assuming that the average number of people per household remains the same, the projected housing requirement = 626/2.22 or 281 households
  4. On an average, Pittsfield has approximately 0.87 housing units per acre. Hence, new land required to accommodate the projected household increase = 281 x 0.87 = 244 acres
  5. According to the Urban Land Institute, the per capita requirement for retail space is 22 square feet. Hence projected retail space = 626×22 = 13722 square feet or 0.31 acres

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