Math 151 , Day 14, Wed., Feb. 27, 2008 Hit Reload...after class.

HW Day 14: Read Ch. 4 (Scatterplotts and correlation) to p. 99 Check p.105  4.12, 13, 14,   and  for the next class pp. 99-105 (correlation) Check 4.14 thru 4.20.  You do not have to be able to calculate r by hand.  You should be able to guess roughly at an r for a swarm of data; as p.102, eg. 4.6, and know and  be able to use facts 1-4, p. 101, and cautions 1-4 p. 103.
Please also , Ch. 5, Regression, thru p. 125 (check p. 137: 5.14 through 20, basic line and regression line facts and tools. 21 r and slope, 22 is harder--changing units--don't worry about it. 23 If you sketch the graph and draw a line thru the points, you should be able to guesstimate the slope well enough to choose among the 3 answers.) ahead: Continuing regression, p. 126-137.

Hand In Fri. (yes) Chapter 4 intro: : 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?(Keep a copy of the graph, to use in the next hw.) p. 107 4.23 reading ability - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Scatterplots using SPSS. Get Scatterplot handout, outside my door, or link. (check download for corrections). Please email me with any other SPSS difficulties or discoveries! ---From now on, make all scatterplots on SPSS!  Don't forget to check Measure, and to add Labels.  (Trouble printing? Try copy/paste into Word, printing in Word.  If you print from Word, on a computer without SPSS, symbols may look funny.  'S OK.) Governors' Salaries HW, accompanying  Scatterplot Handout (check download for corrections) handout and govsal_vs_pay.sav  data file. Use SPSS and answer questions 1-5.   Do these questions on a separate page, and Keep till we have finished all 12 questions! p. 96, 4.4 and 4.5 (SPSS) bird colonies(Save your file; you'll use it again for 4.10) 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. (Keep a copy of the graph, to use in the next hw.)

Read, to discuss    Correlation: Look at all the graphs you make, and guesstimate the correlation coefficient (before you read or calculate it.)

Optional  Do now (for Ch. 5) if you need the practice: Straight line graphing practice: A.  y = -10 + 3x, graph for 2<x<10. B.  y = 500 - 20x, graph for 0<x<10.

Leftover: one of the locomotive problems had a z = 4.5--off the end of the table!  What happens further out in normal tails?  Almost (but not quite) 0.  (Handout last time   p. 80-81 3.11 and 3.12 (locomotive adhesion, 2 dist's)  )
HW Questions?  backward problems?  Going from area to x: Day 11,   Recap Day 12,   Normal probability practice 
= = = = = = = = = = = = = = = = = = = =

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)= predictOR
  response =    dependent = "y" = vertical axis      = ("effect ") =predicteED

(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)

Get SPSS Scatterplot handout, link.  (check download for corrections) +  Governors' Salaries HW sheet,or outside my door, if you missed class. (BPS Ch. 4&5)
SPSS:   Graphs>Legacy Dialogs>Scatter/Dot > Simple Scatterplot.  Move variables from the lefthand  list to the X-axis (horizontal)  and Y-axis (vertical) boxes. See Handout (check download for corrections) for more.  Files from text? Don't forget to check Measure, and to add Labels.
We discovered in class that If you have a labeling variable (like names of states), you MUST move it to "Label Cases by" box when you create the scatterplot, for it to be available when you are in the Chart Editor.
  Some scatterplot data:  educ-v-mortality.sav  ,   studatsp03.sav .   govsal_vs_pay.sav  is the file used for the handout.
(BPS Ch. 4&5) 

Correlation: (pp. 98-105)  The (Pearson) correlation coefficient r is a numerical measure for how strongly linear (and in what direction) the relationship is.  Doesn't substitute  for a scatterplot.
Use if data is:  2 quantitative variables, & "nice":
    One cluster/cloud/band.
   Pretty straight.
   Outlier(s)? Do with/without & be cautious.
Correlation experiments:  Website,  http://www.whfreeman.com/bps4e,"Statistical Applets",  Correlation/Regression.  Play with data points, observing the Correlation Coefficient.   Check in the "Show Mean X & Mean Y lines" box.  See how much is in each quadrant. Compare with correlation coefficient.