Math 151 , Day 12, Wednesday, Sept. 20, 2006 .After class

Hand In Friday: NOTHING.  All postponed.  Day 13 will be this plus probably some more p. 92, 4.1 explanatory/response or just association     4.2 expl/ resp in an experiment (coral)     4.3 beer and blood alcohol, other variables p. 108, 4.24 date heights Make the scatterplot by hand.  Answer these questions instead of the ones given:  Describe the relationship--form, direction, strength,  (with only 6 points there's not enough data  to talk about outliers).  Is there any female dating a male shorter than she is? p. 107 4.23 reading ability - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -   Scatterplots using SPSS.  Scatterplot handout is outside my door (white folder) if you want to work ahead. ---From now on, make all scatterplots on SPSS!  Don't forget to check Measure, and to add Labels. SPSS Scatterplot Handout:  Use the handout and govsal_vs_pay.sav  data file to use SPSS and answer questions 1-5 (page 3 of handout). p. 96, 4.4 and 4.5 (SPSS) bird colonies p.96, 4.6 (SPSS) gas mileage p. 98 4.7 (SPSS) icicle growth. Data is in table 4.2. Be sure to write on your graph which group is slow water and fast. p. 109 4.25 a, c (not b) (SPSS) running records, M/F These are record breaking times, so a year without a number is one in which the best time was slower than the last record.

Read, to discuss

Optional  Straight line graphing practice: A.  y = -10 + 3x, graph for 2<x<10. B.  y = 500 - 20x, graph for 0<x<10.

Exams back next time for sure!  Sorry!
SPSS comments. 1) More is not better.  Snowstorms of graphs and tables are not the point.  Make the one graph (or 2) that address the issue.  Find the summary values you need.  Discuss.  Don't throw in un-discussed or irrelevant stuff.
2) What goes wrong with scale (quantitative) data labeled categorical?  Solutions, p. 2  The numbers become just labels; the ruler line becomes a list of labels.
HW Questions? 
  Handout: Normal probability practice  (Parts are here)
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
<>Using z tables to go between raw values and proportions (percentiles)  See Day 9
Spent class on Normal--No new material covered.  Start here Friday.
 --What proportion of pregnancies last 310 days or more?  z = (310-266)/16 = 44/16= 2.75.  Area above 2.75 = .0030.
        3 in a thousand pregnancies last that long.  Pretty rare.  Is "San Diego Reader" one of the 3-in-a-thousand, or is she lying?  (this is the kind of question we deal with in Significance Testing, part 3 of the course).*
= = = = = = = = = = = = = = = = = = = =
Relationships: (BPS4e Ch.4, at first to p. 98)  
Two Related quantitative variables  (We used side by side stemplots, boxplots, histograms to relate a quantitative variable to a categorical variable)
    "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)
Form (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. (BPS Ch. 4&5) Pages 1-3, Page 4
govsal_vs_pay.sav  is the file used for most of the handout.