It's not about the bias per se

Statisticians have an eye for bias in unlikely places. I came across a nice example on the Linkedin feed via Mary Kate Stimmler. She showed the chart shown above.The proportion of U.S. adults who have college or higher degrees rose from 14% in 1975 to almost 40% in 2023.The linear trend is so very clear. How can a statistician nitpick this?Well, we can and we do. The issue with this analysis is that it didn't adjust for the change in the age distribution of the underlying population. Between 1975 and 2023, the proportion of the population who's 25 and over probably increased substantially, as is the case in most developed nations.Based on some feedback, she made the following alternative chart:She concluded that the adjustment didn't make a difference in this dataset.Instead of an adjustment, she applied what is called "conditioning". The revised chart only concerns the age group 25-29. It shows the proportion of this age group that has college degrees or higher. We have to be careful…