The averages you are looking at for Oregon are different because the average for all of 2011 combines information for all months so far, while the chart ending in February 2011 is just for that one month.
The CarInsurance.com Premium Index (CPI) chart shows that for the one month of February the average rate was $1172 while the average for all of 2011 so far (which at that time would have included two months, January and February) was $1159. That is why you see a difference in price.
The CPI chart now includes March which had a monthly average of $1136 in the state of Oregon and this brings the 2011 average for Oregon to $1151 so far this year.
The CPI is a broad indicator of pricing activity in the personal car insurance marketplace, it is not a comprehensive index as it reflects only the quotes of companies CarInsurance.com represents in the 49 states plus the District of Columbia.
The CPI study reports the lowest average annual auto insurance rates quoted to consumers that compare rates at CarInsurance.com. This index chart rates that consumers viewed, but didn't necessarily purchase. Rates come from car insurance rate quotes consumers receive from over a dozen of the nation's leading auto insurers.
The CarInsurance.com Premium Index outlines the lowest average premiums for car insurance holders and is broken down by State, Year and Month. So the average for each state is found by the information brought in from rates quoted to drivers for that state during the noted time period, such as January 2011 or for all of 2011 thus far.
Average rates on the CPI may be more accurate for some states than others. For instance, states for which data is only available for limited months may skew slightly higher than the true state average for auto insurance premiums.
Here at CarInsurance.com we offer the ability to shop for car insurance online and the ability to purchase your policy directly through CarInsurance.com, so get started with instant car insurance quotes for Oregon or any other US state.