Parity progression ratios are a useful tool in analysing fertility trends. Brass (1985)
described a method of using the current distribution of age-order specific fertility rates
to estimate the future trends of parity progression ratios, commonly known as the
projected parity progression ratio method. The major output of this approach is an
indication of the future trends in fertility by parity, on the assumption that current ageorder
specific fertility rates continue to apply until the end of women’s reproductive life.
The objective of this study is to assess how well the projected parity progression ratio
method works when applied to two successive censuses or Demographic Health
Surveys. Four countries, namely Malawi, Zimbabwe, Cambodia and Panama, each with
two recent censuses which are ten years apart, are used. Each of the census and survey
used is taken through a data quality assessment process to check for inconsistencies.
Using age-order specific fertility rates derived from births in the past year, parity
progression ratios are projected to the next census. These results are compared with the
actual parity progression ratios obtained in the second census for each country. The
application of the projected parity progression ratio method to the Malawian and
Panamanian datasets resulted in a relatively good fit whilst for Zimbabwe and
Cambodia; the method did not produce a good fit. The results of the comparison show
that the method produces a good estimate of parity progression ratios when the age
pattern of fertility remains relatively constant over the intercensal period. The study also
reveals that the method is dependent on the quality of the data used. A suggestion for
future research is to improve the method assessed through allowing for a gradual shift
in the age pattern of fertility for populations with rapidly changing fertility. This can be
done by designing a model that allows for a change in the additional proportion of
women expected to attain specific parity by the end of their child-bearing period.