Table 3.

Constructed socio-economic status (SES) classification (modified Kuppuswamy classification)

Level of Education	Assigned score
Higher education (level ≥ 12*)	6
College (level 6 to 12*)	5
Primary school (level 1 to 5*)	3
Informal education (i.e. self learning); literate	2
No formal education	1
Occupation
Professional and skilled	4
Business, household keeper	3
Retired/unemployed	2
Semiskilled and unskilled	1
Household income
Income covers expenses; no loans needed	4
Income does not cover expenses; no loans needed	3
Income covers expenses; loans needed incidentally	2
Income does not cover expenses; loans needed regularly	1
Socio-economic status scale	Summed score
High	9 - 14
Middle	7, 8
Low	3 - 6

*Education levels based on the Vietnamese classification system