MATH 251, Probability and Statistics I, Fall 2005, Sept. 12 Day 8After class, added HW.

Handout  Scatterplots--SPSS...

Hand in: Scatterplots (ch2.1) p. 112ff, mostly Continue to watch for data variables with the wrong Measure in SPSS. Using SPSS:  2.6 Muslim literacy (note, table 1.2) 2.14 speed/fuel  Also Insert>FitLine>Smoother for this set. 2.13 body mass M//F (use sex as the Legend Variable)  2.16 icicles 2.18 nematodes   Use Dot-line (handout p.2 top) to get means line.  Sometimes by hand it's convenient to use medians instead of means; easy to estimate in the picture.  BY HAND, Mark the medians for each nematode level and connect with a dotted line.  How different are the two lines? On a separarate sheet:  Begin the Governors' Salaries HW (p.3, Scatterplot handout.)  You can do 1-5 now.  KEEP till all questions have been answered.

Read, discuss  p. 112, 2.1, 2.2

Optional  2.7 breeding merlins,  Make the scatterplot by hand if you need the practice.

Normal Quantiles (day 7).  Another way to get the plot: Analyze>Descriptive Statistics>Explore: Plots: Normality Plots with tests.  Here the "Expected" axis gives you standard normal numbers.  If you use Graphs>QQ, you get raw numbers on the "Expected" axis.
Relationships: (Ch 2 Intro and Sec. 2.1)   Handout  Scatterplots--SPSS...
Related quantitative variables
    "Just Related" or "explanatory & response?"
(scatterplots)
explanatory = independent = "x" = horizontal axis ( = "cause", sometimes but not always)
  response =    dependent= "y" = vertical axis      = ("effect ")

(Living histograms:  Height vs. weight, Height vs. gpa)

Discussing Scatterplot
General Pattern                                      Deviations
Clusters?                                                      Outliers? (label if possible)
Shape (linear, curved, ...?)
    Strength of relationship (how unfuzzy)  "Weak, moderate, strong"
Direction
    Positively associated:  y increases as x increases (generally).
    Negatively associated:  y decreases as x increases.

Mark subgroups differently to do comparisons. (Subgroups defined by categorical variable, like Sex, Region of country)
  Some scatterplot data:  educ-v-mortality.sav ,   studatsp03.sav
Handout on SPSS Scatterplots etc. (Moore Ch. 3)
govsal_vs_pay.sav  is the file used for most of the handout.