SES is usually measured through educational level (low-middle-high), income (e.g. quartiles) or occupation (e.g. white-collar vs blue-collar jobs). Educational level is probably the most straightforward and most widely used one. It is not a perfect indicator (some may have a good socioeconomic position in spite of having low education or the other way round) but it has shown to be quite accurate in most countries.

thanks Lluis.

how do you sub-categorize the education level?

under 12? 12-18? and more than 18 years?

That depends a lot on the country. I would suggest to check previous studies and categorize accordingly. Good luck!

Hi! this is a very intersting paper about the topic, take a look!

Article Indicators of scioeconomic position (Part 1)