Project 39
Project description

In Project 23, we used simple linear regression to investigate whether it rains more in Tacoma than in Seattle or Portland. Now investigate this question in the broader sense of: it rains more in a city if the mean difference in annual rainfall is greater than 0, the difference in annual rainfall being the annual rainfall of that city minus the annual rainfall of the other city. With this interpretation of “raining more”, compare:

  1. Portland and Seattle rainfall.
  2. Portland and Tacoma rainfall.
  3. Seattle and Tacoma rainfall.

Background on the data set

This data set gives annual precipitation totals for Portland (OR), Tacoma (WA), and Seattle (WA) for the years 1966-2006, precipitation being defined as: "Any form of water particles-liquid or solid-that falls from the atmosphere and reaches the ground."

Data Source: Western Regional Climate Center (, specifically "Monthly Totals" under "Monthly Precipitation Listings" for the following: Portland, Tacoma, and Seattle. The definition of precipitation quoted above is also from this website, specifically in their climate and weather terms glossary. (All links accessed June 14, 2008.)

Variables in the data set
The variables in the data set are as follows:
year(years)year of precipitation measurement
cityPortland, Seattle, or Tacomalocation of measurement
precipitationinchesamount of annual precipiation
Link to the data set
The full data set in csv format is at: