Alan Greenspan in his role as the chair of the Federal Reserve, changed the way inflation was measured.
His thinking was that when the price of steak got expensive, people would switch to eating chicken. By eating chicken it lowers the cost of living. While this is true, the substitution of chicken for steak violated the concept of measuring a constant standard of living. The CPI now has many substitutions. < YouTube by John Williams >
One concern The Fed had was the volatility in the consumer cost of living. The “problem” was the cost of food and energy went up and down so much it was influencing the overall cost of living. The solution: remove food and energy from the CPI.
The Fed has since changed from CPI to PCE, the Personal Consumption Expenditures Price Index, but it pretty much tracks with CPI.
If you are interested in the real inflation rate, John Williams from Shadow Stats offers a detailed view of what the inflation rate would look like if it were tracked using 1980 and 1990 government techniques.