Population Projection: Calculation Process

You can obtain from me a population projection template, POP PROJ, which is composed of six worksheets: One worksheet, Input Formats, provides the data for the remaining five, Output Formats. The five Output Format Worksheets are structurally identical.

The Input Format Worksheet is a matrix in which each row represents a five-year age-group cohort, with the exception of the topmost cohort which includes everyone 75 years of age and older:

Input Formats for Cohort Survival Population Projection

CURRENT YEAR …………….

          CURRENT  MALE   MALE   CURRNT FEMALE FEMALE  BIRTHRT

           MALE   SURVIV MIGRATN FEMALE SURVIV MIGRATN PER1OOO

COHORT      POP    RATE   RATE    POP    RATE   RATE   FEMALES

----------------------------------------------------------------

75+

70-74

60-64

65-69

55-59

50-54

45-49

40-44

35-39

30-34

25-29

20-24

15-19

10-14

5-9

0-4

TOTAL     xxxxx                 xxxxxxx

GRND TOTL xxxx

M/F RATIO ....

The first three columns provide information about the three key variables for males, the next three provide parallel information for females. If you wish to examine the effects only of natural increase or only of migration, do not set the other variable to "0." Rather, enter a value of "1.0" to eliminate a variable's influence. The seventh column provides information about the birthrate for females in the childbearing cohorts. The specific definitions of survival rate, migration rate, and birthrate have already been provided. You are also asked to specify the beginning year for the analysis. This information is used to label each output table with the appropriate year. You are also asked to enter the ratio of males to females in the birth cohort (i.e., enter the proportion of the cohort that is male). The worksheet will tally the male and female population and the total population. You can use this to doublecheck the accuracy with which you entered the data for each column.

The spreadsheet uses the input formats to calculate five worksheets: one displays the current population, and the other four present a twenty-year population projection at five-year intervals. Each projection displays the population by sex for each cohort. Total population by sex and total population are also calculated.

Recall the process by which a cohort moves from age group to age group: The migration and survival rates are applied to the current population in an age group, and the results are entered for the next time interval as the population in the next oldest age group. The survivors and net migration from the oldest age group (75+) is added to the survivors and net migration for the 70 - 74 age group who enter the 75+ age group at each interval.

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