What is the best way to measure deprivation among students?

The Scottish government wants a fifth of university students to come from the most disadvantaged parts of the country by 2030.

The headline measure being used is the applicant's postcode area.

This is based on data from the Scottish Index of Multiple Deprivation (SIMD), which highlights the challenges facing the area - including income, poverty and unemployment.

But, of course, it does not follow that the applicant who lives in such an area is disadvantaged personally.

Earlier this month it emerged that a very small number of university students from the 20% most deprived areas (SIMD 20) had attended independent schools.

This meant that they would count towards a university's numerical target to widen access, although there is no suggestion that the applicants were given any special help to get in.

So if SIMD 20 is an imperfect measure, is another broad brush measure available instead?

There are no simple answers.

This may sound fairer but is potentially more complicated than it sounds.

Current parental income could be misleading as a measure of a disadvantaged upbringing. The main breadwinner may have recently lost their job or retired.

It would also mean applicants having to provide information to the university admissions service which they do not currently have to give.

This certainly would indicate financial disadvantage. However some older children may not take up free school meals.

To directly equate the fact a child only lives with their mother or father with disadvantage almost sounds like moralising.

Many single parents who are widowed, divorced or whose long-term relationship broke up would almost certainly resent any implication that their child was disadvantaged by this factor alone.

Obviously some children who grow up in single parent families do face genuine hardship and disadvantage. There are very real issues, for example, surrounding the availability of childcare to allow a single parent to return to work.

But, of course, other single parents hold down good jobs and are able to rely on their extended family, friends or professionals to provide additional childcare.

Living in a rented house should not be confused with living in temporary or substandard accommodation or living on a "sink estate".

By historic standards, a relatively large proportion of Scots now own their own homes. In the 1980s and 90s, many became the first in their families to own property when they bought their council house. Before then many who lived in the best council houses might have been thought of as "skilled working class" or "lower middle class".

However that does not mean for a moment that someone who lives in social housing today could automatically be considered disadvantaged.

In some places, the price of property would make it hard for many people with good jobs to buy a home. Meanwhile the right to buy council houses has been abolished.

The huge growth in student numbers in recent years means this would be misleading and is no measure of personal disadvantage.

Until the 1990s, university education was seen as a privilege. Many middle-aged people who hold good jobs got their first job straight from school or attended colleges or polytechnics.

Some experts have argued that a good measure to use may be to cross-refer two different factors - for instance living in an SIMD 20 area and being in receipt of either free school dinners or an Educational Maintenance Allowance.

This would make it more likely that the SIMD 20 applicants being counted towards any targets were personally disadvantaged. Universities Scotland would support this.

It is broadly accepted that widening access to university is about more than a home postcode - even if SIMD 20 is a useful measure as a policy objective.

For instance a child in any area could have faced all manner of difficulties which affected their school performance - poor health, physical disabilities, the death of a close relative, their parents going through a difficult divorce.

One of the key steps being taken by universities to help them meet their widening access targets is to pay less attention to exam results in isolation - so-called "contextualised admission".

That way they pay more attention to the applicant's own experience and potential or any specific factors which the applicant faced.

SIMD 20 is only part of the story of disadvantage itself.