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The International Journal of the Royal Society of Thailand
Volume XII, 2020

Appendix

Strengths and weaknesses of the PIT sample provided by the Revenue
Department, Ministry of Finance, Thailand

The sample

This is the first time since the introduction of the personal income tax in
Thailand in 1932, that the Revenue Department provided a sample data set
from the tax returns for personal income tax for any researcher or institution
outside the Ministry of Finance.

RD provided separate 0.3% samples of PND90 and PND91 returns for
2012 as recorded in the department’s databases, selected from a total of
2,244,006 records (PND90) and 7,506,923 records (PND91). The records were
sorted by province based on the taxpayer’s contact address and a separate

0.3% sample was selected randomly from records for each province.
The sample records provided for analysis by the researchers have been
‘cleaned’ by RD and include 63 fields (columns) for PND90 and 46 fields
(columns) for PND91. The information provided for each record includes
amounts of gross income, income after deduction of exemptions and expenses,
allowances, income after deduction of allowances, contributions and donations,
taxable income, tax credits and tax due with totals by type of income, allowance

and donation distinguished on the tax form.
To accompany the sample records RD provided files with record counts

and summary statistics (means, standard deviations and variances) by province
for each column in the complete set of records in the department’s databases
together with the same statistics for records in the 0.3% samples and a data
dictionary describing information in each column.

Strengths
The clear format and presentation of the sample records with comparative

summary statistics for the full databases gives researchers grounds for
confidence that the samples provide a realistic picture of the pattern of income,
expenses, allowances and tax assessments in the country as a whole and the
summary statistics by province imply a high degree of uniformity in tax

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Francis Cripps and Pasuk Phongpaichit

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