Math 151 , Spring 2005,  Day 22 Monday March 28 Hit reload ...

Exam 2 this Friday (Day 24, Apr.1).  Covers thru today's HW (but no more than Part III).  Let me know by Wed. if you need a special time to take the exam.
How much computational detail from part II?  You don't need to know the formula for the correlation coefficient, but you should be able to guess roughly the r from a scatterplot, and know and use the properties pp.121-2.You will need to know, among other things,  how to find b₀ and b₁ from the means, standard deviations, and r of the x-and y-values,  and to give the formula for the regression line, (like 17, p.154); and to graph the regression line on top of the scatterplot.  Also find by hand the value that the line predicts for a particular x.  You should be able to identify and calculate the residual value for a particular x-y point as its vertical distance from the line (negative if the point is below the line), and identify and understand potential influential points.  You should know  that the regression line goes through the point given by the two means, and that the  regression line "rises" r standard deviations in y for each standard deviation increase in x (pp. 137-8); also that the regression line of "weight" on "height" is not the same line as the regression line of "height" on "weight" . You should be able to describe verbally the meaning of R² in the context of a data set.

Day 22 (Mon. March 28): Reading: D&V Ch 12, 13. Review part III p. 262.  AS13.  Bring questions; Parts II and III 
    Next, D&V Part IV: Ch. 14, Ch.15 thru p.  291 (then Ch. 18 &on.) ActivStats is very good for part IV--Ch11 shows Law of Large Numbers as D&V express it. Ch14, 15 correspond well with the text and present very good examples.

Hand in  Chapter 13, p257ff.  1,2,4,5,6,10,11,12 You did the "observational study" ones, and started the "experiment" ones. Finish these for those that are experiments, for all that are Completely Randomized, & add 17 (postpone 18) .  32 Shingles  a,b,c (postpone d) 36 Washing clothes  From Review part III, p. 263ff. 26 Laundry 34 Pubs A. Do the Chart experiment-- ActivStats 13-3, first activity.  Save your data with your name on the file, remembering where you saved it.  Do the next two SPSS activities, on that page. (One error in the tutorials: Your files are NOT of type .txt; they are of type .dat.  Safest--use "all files" to locate them.)  Hand in the graphs you made, writing what results you see and whether you think they are "statistically significant". B. REDO the assignment on the handout Using SPSS to find a Simple Random Sample, this time doing Transform> Random number seed>    Make sure Random Seed is selected, and click OK. first.  Also: Find the mean  duration, for your sample, and for the whole set..   Bring to class to pool your results.     More here on seeds.

Read,   to  discuss      Review Part III: p. 263 ff: 1 thru  17 odds,  +12, 18

Op- tion- al

Homework questions? Day 21
Chapter 13: Experiment: Continue Day 21   Brief summary:   All about avoiding BIAS
Principles of designing a comparative experiment (p. 243)

• Control: Control sources of variation other than our factors, by making everthing else exactly the same. Use specific levels of the factor, same within each group. (unfortunately, limits generalizing to other levels not used)
• Randomize the assignment of units to treatments: reduces possibility of confounding some characteristics of exp. units with the treatments.
• Replicate:  In the single experiment:  replicate the treatments on many exp. units:  Reduce the chance of unrepresentative results, assess the variation within a treatment.
   (Replicate the entire experiment in another time, place, setting, on another group.)


• (Block--not required:  Like stratifying--break into like blocks (M/F, age groups), then do above within each block. )