Table 1 presents some variations across the four datasets used in this study in terms of sample sizes,
geographic regions and sampling methods. For example, while both the Poovatanikul (1993) data
and the Ratchaneeladdajit (1997) data were collected from the Bangkok area using random sampling,
the other two datasets were focused on other regions as well, but not based on random sampling.
Despite the variations, the four datasets commonly used the PIMRS-Thai Form and included secondary
school principals. Notably, the comparison study employed data collected from a sample of 1195
Thai principals (primary, secondary and K–12) in 2008. Although not randomly selected, the sample
was roughly representative of the Thai population of principals by geographic regions and included
large numbers of primary and secondary school principals (Hallinger and Lee, 2013).