GDP per person. GDP is an attempt to measure the value of all finished goods and services made within an area over a period of time. There are multiple ways to measure it, and most final estimates are a mix or average of methods.

GDP measurement has flaws in terms of it's absolute value, but it's flaws are generally thought to be somewhat consistent. That is, if GDP doesn't capture some element of value well, it's going to consistently fail to capture that element, so changes in the value are still meaningful unless they occur over time scales where those uncaptured elements vary dramatically.

An example of a potentially unaccountable element is the value of "home-makers" or "stay at home moms" that were once far more prevalent than today, and provided value to households in a way which was not measured. Comparing GDP changes over one year is not going to be influenced much by changes like this, but comparing over 50 years it becomes noteworthy.