Project 79
Project description

You may assume that the annual rainfall data in this data set is a simple random sample from all the years (past, present, and future) of the past century and upcoming century. This is manifestly far from true, but it is a simplifying assumption that we make for the purposes of modeling here. Find a 95% confidence interval for the mean of the annual rainfall in Tacoma minus the annual rainfall in Portland during this time period.

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: