The parity structure of fertility decline in Thailand 1953-1979.

Researchers fitted sample data on 15-65 year old women from the 1970 and 1980 censuses of Thailand to the model fertility curve of the extended birth history reconstruction procedure which looks at duration since 1st marriage specific fertility rates and age at marriage as the minimum age of women at conception. This study actually covered the period 1953-1979. Considerable underreporting of children ever born occurred in the 1980 census but mainly among women of at least parity 5. This found a substantial decline in progression from parity 0 to parity 1 during the late 1960s and the 1970s. Further the period progression ratios from parity 0 to 1st marriage and 1st marriage to parity 1 fell with time especially parity 0 to 1st marriage. During the study period family size fell to mainly 2. Some families did complete family size at 3 children however. The researchers observed that in the 1980 census 2299 women out of 43848 reported own children born before the women married. This finding made the researches question the quality of the age data and/or the applicability of the extended procedure since it assumes no fertility before 1st marriage. They did no exclude these women however when the calculated the period progression ratios for progression from 1st marriage to parity 1 since that would introduce bias in the results. Thus the results for that progression would have not been parallel to those for the other progressions. In conclusion the significant decline in the number of Thai women who had a 1st marriage and then a 1st birth between 1965-1979 contributed considerably to the fertility decline in Thailand.