Time did not allow: Sec. 7.2, comparing 2 means.
Handout, Two-sample t procedures ...two independent samples (how
to do it on SPSS)
The homework involving this is up, Day 39
You can go ahead and get the SPSS output you need, now...
How to do it will be covered Friday.
~~~~~~~~~~
HW: If you missed class, SPSS handouts will be outside
my door.
Reread 7.1. Review Sec. 3: pp 195-6 for Matched pairs, pp. 186-191
for two-sample t. (Three or more treatments require analysis
of variance, Ch. 10. Not in this course.)
Read ahead 7.2. You are responsible
for the material through p. 402; should read and understand the rest
in order to be able to deal with the output from SPSS, and future encounters.
You don't need to know the formula for
d.f. on p. 403, only that SPSS uses it to produce the "equal variances
not assumed" result. You would never try to calculate it by hand--too
much possibility for a mistake..
You don't need to know the "pooled two-sample t-procedure", only that
it goes with the "equal variances" line in the SPSS results--we prefer
to use the "equal variances not assumed" results in all cases. You
should know that you will still meet the "pooled" procedure as the "standard"
in older books, or areas where the newer method has not filtered
down yet.
| Hand-in
--Go through Example 7.4, p. 99, in the SPSS manual ( Example 7.3 in BPS, p.375). Produce (& Hand IN) the two outputs I put on the handout under Matched Pairs: Testing using the "Paired Samples T-Test" procedure on the original variables, and Testing using the "One sample T-Test." Compare with the text analysis. p. 374 7.7 DDT do this again on SPSS.
Compare your results with those you got by hand.
Matched pairs : you just treat the difference/change as one variable (x). p.378, 7.9 &10 (right/left threads) Also, make a variable for the difference and produce a stemplot to check for outliers. * There is an annoyance here--we expect the right thread times to be smaller than the left thread times, so it might be easier to think about (left -right) and anticipate a positive average. But unless we exchange the order of the variables in the SPSS file, we have to do (right - left) if we do a "paired-sample test", and anticipate a negative average. Be clear what you do. p. 382, 7.11 caffeine dependence Again, watch out for the direction of your differences and what they mean. |
Read, to discuss | Optional
Review: |
| Sievers home | Math151-Sp01/Day38.htm | 4pm | 5/2/01 |