The CPI definitions change to reflect consumption habits. In any case, CPI definition changes don't affect your perceived inflation or effective return -- it's

The CPI definitions change to reflect consumption habits. In any case, CPI definition changes don't affect your perceived inflation or effective return -- it's just trying to measure what you might be feeling. CPI affects Social Security payouts, that's a different thing than investment returns (but obviously does affect the well-being of seniors). CPI probably does understate perceived inflation for seniors. There is an index specifically for seniors (CPI-E) that has more healthcare in the basket of goods, and it's higher.