Uses of national income data

What are the uses and limitations of national income data to assess living standard over time ?

Think about it: what happens when someone's income increases? That should answer your questions if you apply it on a national level.

BUT that's the thing , sadly don't understand national income = national output = national expenditure

No interpret it in a more personal level. More money = more consumption of goods. Consumers can benefit from consuming more goods and services, so if consumption levels are high, prosperity will be bigger. Improving in public services, if tax revenues increase, the government can spend more on important public services such as health and education, if the quality of health services improve, the quality of life will improve as well.

Thnx so much :-) but I still need help on that bullet point of the spec

You haven't mentioned about that, or even the subject you're doing (I've assumed Economics/Geography).

Sorry it's economics . I feel like crying as I don't understand that bullet point

Which one? I may be able to help (although I've never done Economics, but have read a few books a little)

The use and limitations of national income go assess changes in living standards overtime

First of all you need to identify what type of data it is and the limitation it comes along with it. Secondly, even if there is a correlation it does not show a causal relationship (increase in national income does not exactly lead to increase in living standards, as many other factors may be involved)., Moreover, although people's living standard may improve, their living standards may have not (due to inflation, so prices of everyday goods and services may have risen).

The data is gdp

Read this website.