Trends in Premiums in the Small Group and Individual Insurance Markets, 2008-2011. Statistical Testing


Statistical testing compared 2011 estimates with previous-year estimates where appropriate. All tests conducted were t-tests with significance determined at the p≤0.05 level. Given that the sample of filings represents a large proportion of the population, variance estimates used in significance testing were adjusted by the finite population correction (FPC) factor. When the proportion of the population in the sample is large, the estimate of the error must be corrected to account for the added precision gained by sampling a larger percentage of the population.

We also conducted an additional set of analyses comparing study dependent variables (such as premium increases) between categories for the same year. For example, we compared premium increases in 2008 for HMO vs. PPO vs. indemnity plans.

Categories include:

  1. State regulatory authority – prior approval, file and use, HMO review only
  2. Market concentration – high, medium, low
  3. Size of carrier – Three largest in the state individual and small group market vs. other carriers
  4. Type of product – HMO vs. PPO vs. indemnity

Although we conducted statistical testing as to whether differences between categories were significant at p≤.05, we do not show the results in the graphics in order to avoid clutter from additional notations. When differences by category – e.g., HMO vs. PPO – are mentioned in the text, they have met the p<.05 threshold.

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