Depending on who you talk to (the federal government or a like-minded individual), the Consumer Price Index (CPI) is either an accurate or inaccurate measure of price inflation, respectively. What is important to understand is that each side stands to benefit from its position. The government tends to understate inflation while a like-minded individual tends to overstate inflation.
In regards to the government, the dollar amount of entitlements doled out by programs such as social security are affected by cost-of-living adjustments, which supposedly reflect an increase (or decrease) in the cost-of-living. As such, the government tends to understate price inflation to save itself money, thereby reducing the cost-of-living adjustment.
In regards to the individual (at least to those who visit this website), price inflation is a constant concern. After all, individuals who understand sound money and free markets know prices should come down over time. However, due to the Federal Reserve (primarily), this is not the case. Thus, we warn against the coming price inflation, and in my opinion, tend to overstate price inflation (without empirical evidence) as a means of reinforcing our argument.