Degree holder salary statistic misleading ?

Hi there, 

I've had a root around but I can't see any discussion on this matter. 

I'm at a unique point in my life where I have the opportunity to study
a degree (having dropped out previously)

Part of my motivation comes from statistics frequently quoted
regarding the enhanced earning power of graduates through their life
time (in the UK its an **average** of £500k, I think)

I wonder if any one has any views as to whether this is necessarily a
good indicator of the value of degrees. Degrees have an in built
process of selection (usually), which filters out
a) People of lower intelligence/ educational aptitude
b) People from lower socio-economic groups (due to cost or perceived
cost)

That is students are predominantly middle class and have higher than
average IQ, where as non-degree holders include the middle classes and
people of higher than average IQ.... AND everyone else (bringing down
the average). So it is not necessarily the degree, which is enhancing
wages, it is the pool of people who subscribe to the program who are
already positively skewed toward greater monetary success.

For me money is not the only qualification of whether a degree is
worthwhile for example it might allow me to enter a profession where I
get paid a similar salary but in addition perhaps gain greater job
satisfaction. However I don want to examine this factor to inform my
own decisions, and any way I’m interested in what people think.

Sorry for the length

Cheers

Jim