Lab assignment 4 (due Monday, Feb. 20)

*** SLBD stands for the book "Statistics: Learning by Doing."  ***

*** EWA stands for "Extended Writing Assignment"  ***

Please read lab session 5 (pages 64-73 of SLBD) BEFORE coming to class
on Monday.

I.  Complete the EWA listed on page 74, taking care to follow the 
grading rubric handed out in class.  The EWA should be typed and the 
writing style should be fairly formal. (In addressing point (2) on page 
74, for the "calibration calculation," discuss your guess and "predicted 
true value" for the 13th landmark.  Did using the prediction equation 
improve your estimate of the actual true distance, compared to your 
original guess?)

You don't have to do the short-answer assignment, but you can use 
the questions in the SAWA to guide what you write in the EWA.  Don't 
worry about the questions that deal with the class's guesses as a whole, 
since you only have access to your own guesses.

II.  When the major variable of interest in a study is difficult or 
expensive to measure, often the investigator will use a related, more 
convenient variable as a substitute.  This surrogate variable is known 
as a proxy variable.  The lab book gives an example of a proxy variable 
for measuring the force of Russian nuclear explosions.  Can you think of
 another situation in which the use of a proxy variable may be 
necessary?  In a brief paragraph, describe such a situation and any 
cautions that should be exercised when using the proxy variable.