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

forms (PND90 and PND91) for the year 2012, referred to as “the RD sample
5
data set”. This has information on income by source, expenses, allowances,
6
donations and tax due with no identification of the filer except the province

of residence.
This RD sample data set has several weaknesses. First, the data are for

one year only, thus we cannot assess changes over time. Second, income tax
coverage is thin in the sense that the system leaves a lot of people out. For
example the number of income tax filers is rather low in relation to the total
employed labour force (about 25 percent in 2012 in Thailand as against
96 percent in the US).
The third weakness is that the data on income from sources other than
employment income are incomplete for two major reasons. One is a result of

the existing revenue code. Tax filers are not required to declare several types of
income including (i) income which is tax exempt such as capital gains on share
transactions and income from foreign sources unless transferred to Thailand in the
year when it was received and (ii) income in the form of interest and dividends,
which is subject to withholding tax (WHT) but is not reported unless the filer
wants to obtain a tax refund (filers in the top tax bracket may not be eligible for a
refund and have no incentive to report the income from these sources). The other
major reason why data in the tax forms are incomplete is failure to report or
under-reporting as, for example, in the case of fees and rent income, particularly
if the income is not received from a corporate entity that deducts and reports
WHT on fees and rents paid, or business conducted on own account with private
customers.

Considering the weaknesses mentioned the idea of analyzing income of
the top 1 percent using the income tax statistics loses some of its force.

Nevertheless, while recognizing these problems, this paper will examine
what the RD sample data set, along with other sources, can tell us about the top

5 PND90 or ภงด.90 is the personal income tax form for those who earn income from different sources
(income categories 1-8). PND 91 or ภงด.91 is the form for those with income from wage and salary
only.
6 For details of the sampling and strengths and weaknesses of this data set see the Appendix below.

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Francis Cripps and Pasuk Phongpaichit

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