It varies based on who you're asking. Conservatives will focus more on household appliances, since they are more prevalent for any given income (particularly lower incomes) since the 1990s than the 1970s. But this ignores the ways that technology makes things cheaper. Those that argue that costs of living have increased, like Elizabeth Warren, will focus on things such as education, health and housing costs. But none of these things have a widely accepted quantitative measure of well-being.
When people give a particular percentage they are probably talking about real median income or real average income. They may also be talking about average wages. A strong argument can be made that much of the wage growth since the 1970s was due to women entering the workforce. If you just look at men, there was hardly any growth.
The ultimate dumbass conservative comment is to rhetorically ask "How many people had a gigaflops computer in 1968?"
