Lake Data Set. The Florida Lakewatch data set is described in Appendix C.1. It contains water quality information on a sample of lakes in North Central Florida taken during 2005. For most of the lakes, total phosphorus level is reported for a summer month and also for a winter month. Does the typical total phosphorus level appear to differ in the two months?

(a) The summer versus winter difference can be expressed as

(1) the simple difference WTRTP – SMRTP,

(2) the ratioWTRTP/SMRTP, or (3) the logarithm of the ratio.
Using a graphical display of each of these variables, decide which could best be analyzed using a t test. (Only those lakes where both a summer and winter value are present can be used.)

(b) For the variable you chose in part (a), how would you express the null hypothesis of “no difference between the winter and summer typical phosphorous levels”?

(c) Carry out the hypothesis test for part (b), and interpret the results. LO.1