This study aims to estimate the number of centenarians—the population aged
100 years and over, and to assess the quality of registration data about the elderly
population in Thailand. Data were taken from population censuses, life tables
constructed from the Survey of Population Change (SPC), regional model life tables,
and records in civil registration. Life expectancies of centenarian cohorts were derived
from SPC life tables. Model life tables of corresponding levels were applied to
determine survival ratios. These ratios were then applied to census population data
for 2000 to estimate the number of centenarians still surviving in 2010. These
demographic procedures yielded an estimate of about 1,700 surviving
centenarians in 2010, which was only 12 percent of the number recorded in official
civil registration figures. The inflated estimates of the centenarian population
recorded by the civil registration system were investigated by in-depth interviews of
the centenarians, village/sub-district headmen, registrars, and relatives of deceased
persons in two selected provinces. Names and addresses of centenarians were acquired
from civil registration and were followed up to evaluate their accuracy. It was found
from this study that incompleteness of death registration and incorrect age recording
were the main causes of the inflated figures of centenarians found in registration
data in Thailand.