I don’t know that there is any way to calculate a median value of GDP/capita. You can look at income distributions and find a median income and compare that to a mean income, which could allow an estimation, but beyond that, GDP is an intrinsically composite number which cannot be easily (at all?) broken down to individual contributions. I assume income is what the parent commenter is basing the median-mean comparison on, but it’s kind of out of nowhere with no explanation.

For purposes of comparing countries to each other and the same country over time, it’s not 30% off. The average skews higher than the median everywhere, so it’ll be 1.3/1.x.

If you have reported median incomes that are calculated the same way across countries and over time, that would be better. But many countries don’t reliably track that data, and the ones that do calculate it in completely different ways.