Improvements in technology also artificially lower the official CPI numbers. Beginning sometime in the late 1990s, US official CPI calculations started incorporating hedonic quality adjustments.
Consider the example of televisions. TVs are far better today than they were 20 years ago. With the hedonic quality adjustment,
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The average TV sold in 2004 cost ~$400, so according to official BLS inflation numbers for TVs, people should be spending only $14.65 on TVs of the same quality today. Of course, there are no TVs costing $14.65 today. In fact, the typical TV sold today likely cost more than the typical TVs sold in 2004.