Very roughly, the value of the SocialWage is calculated by summing the cost of each program, divided by the number of users of that program, for each program an average person would use. So, in other words, how much that person would have to spend if s/he had to pay for the services out of pocket (at the cost they are now).
The value of the SocialWage (at least in Canada) dropped about 30% in the 90s. It will likely go up again now that we are booming. The SocialWage (at least in Canada) tracks the economic healthy pretty regularly.
See also SocialWelfare.