Measuring the change of prices is a difficult task. There is no way to obtain a completely objective overall change in prices. Every measure will have some kind of bias, and can be argued to be over or underestimated.
Over the decades there have been changes in the way the government measures the consumer price index (CPI). One change was to incorporate substitution effects. This means that if the price of steak increases, and people consumer more beef, then beef is now a larger part of the economy and should have a bigger weighting in the CPI. A second change is to incorporate qualitative changes into the CPI. Thus, if the computer speed doubles in 2 years, but the average computer price remains the same, then the CPI will record a reduction in price for computers.
I wanted to take my own measurement of inflation using items that would not be affected by either of these 2 changes. I wanted to see how much smaller the government inflation number is compared to the modified CPI number. I also wanted to see if there was a change from decade to decade from the 60s to the 2000s, to see if there is an increase in the difference between the two numbers over the decades as the government implemented more changes.