In: Statistics and Probability
Every few years, the National Assessment of Educational Progress asks a national sample of eighth-graders to perform the same math tasks. The goal is to get an honest picture of progress in math. Suppose these are the last few national mean scores, on a scale of 0 to 500
. Year 1990 1992 1996 2000 2003 2005 2008 2011 2013
Score 263 266 272 273 277 278 280 286 288
(a) Make a time plot of the mean scores, by hand. This is just a scatterplot of score against year. There is a slow linear increasing trend.
(b) Find the regression line of mean score on time step-by-step.
First calculate the mean and standard deviation of each variable
and their correlation (use a calculator with these functions). Then
find the equation of the least-squares line from these. (Round your
answers to two decimal places.)
ŷ = + x
Draw the line on your scatterplot. What percent of the
year-to-year variation in scores is explained by the linear trend?
(Round your answer to one decimal place.)
%