Math 151 , Day 10, Monday, Feb. 19, 2001

Wednesday bring questions for exam.
--Exam 1 Friday, in class, closed book.   Bring a simple calculator. I will give you copies of the Normal table.
Covers through 2.1.  You will need to read SPSS output, but not tell how to produce any. You will need to calculate "by hand" a standard deviation for four numbers. (As well as medians, quartiles, etc.)   Problems like HW + some true-false or multiple choice types.
--I will be out of town Thursday-Tuesday.  Prof. (Mr.) Shilepsky will give the exam and the Monday class. His Office: Mac 106, x3262, ashilepsky@wells.edu.
--SPSS examples of Normal data.
--HW questions on "backwards" normal.
--What proportion of pregnancies last 310 days or more?  z = (310-266)/16 = 44/16= 2.75.  Area above 2.75 = .003.
        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).*

Scatterplots:  See Day 9

Correlation (2.2) Discussed day 11
The correlation coefficient r is a numerical measure for how strongly linear (and in what direction) the relationship is.  Doesn't substitute  for a scatterplot.
  1. Measures relationship--same whichever variable is on the x-axis
  2. "Correlation" --only for 2 quantitative variables
  3. "Unitless"--original measurment units are "standardized out"
  4. Sign of correlation coefficient matches direction of relationship
  5. Between -1 and +1.  0: no linear relationship, + or -1: perfect straight line.
  6. Does NOT give info about curved relationships.
  7. NOT resistant to outliers--quite sensitive.

Finding Correlation r in SPSS is embedded in a bunch of output we'll use for 2.3, so we'll wait on it.
Get HANDOUT  on Subgroups(need for p. 95, 2.13, and later)
HW Day 10:
Read Ch. 2 (Examining relationships), pp. 78-91.  Read  2.2 (correlation)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.101, fig. 2.9, and know and  be able to use facts 1 thru 7, p. 100
Hand in  with Day 10
Relationships & Scatterplots: 2.1
p.81, 2.1 (rel. or explan/resp) 
Do 2.17a, p.98, graphing by hand! 
-From now on, make all scatterplots on SPSS! 
-Go through the Using SPSS for BPS Chapter 2 handout. No need to hand in your graphs from that. 
p.87, 2.6 (SPSS) gas mileage
p.89, 2.7 (SPSS) metabolism Using the pre-made data set, graph the males and females simultaneously.  (Use the handout.) If you want to print just the females, change the male points' color to white.  Save your data file and output file for problem 2.22, later.
p. 91ff, 2.8 gpa vs. IQ 		 Read, to discuss 
 
 
 
 
 

 

 Optional (more practice) 
 

 
Hand in 
(This problem looks forward to Sec. 2.3, sort of)  p. 95, 2.13 corn plant density Notice how the data is entered for SPSS--not as displayed here!  Use the top of the Subgroups  handout to see how to get means for the separate planting rates. (Or do them on your calculator.  By hand, mark them on your graph and draw the lines .) 
= = = = = = = = = = = = = = = = = = = 
Do with Day 11
2.2 Correlation (no SPSS)
p. 102 2.18  thinking about correlation.
2.19 men two years older
2.20 r =0, strong assoc. (By hand is fine) graph the data (speed on the x-axis). Draw a horizontal line at the mean of the y's (26.8 MPG) and a vertical line at the mean of the x's (40 mph).  For each data point, draw a dotted line from the point horizontally to the 40 mph line, and another line vertically to the 26.8MPG line.  Use this picture to explain as best you can why the correlation is 0. 
p. 105 2.26  newspaper
2.27 investment diversification
p. 157 2.90 education/age		 Read, to discuss 
(Review) 
p. 82, 2.3 (Breast CA vbles)
 
 
 
 

= = = = = = = = = = = = = = = = = 
p. 99 Use data of 2.17.You graphed this last time.  Guess what r is; look in the back of the book to see how close you got.
p. 106 2.29 blunders

 Optional 
(Review) 
p. 92, 2.9 hotdogs&sodium
2.11 Wine vs. heart disease
 

= = = = = = = = = = = 
 
 
 

 

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*Bear in mind that there were around 400,000 births in California in 1970. (I'm guesstimating.  There were 605,694 births in 1990, and the population of California in 1970 was 2/3 of that in 1990).  So a 3-in-a-thousand event would occur in 3x400 = 1200 births--there would be 1200 women in San Diego Reader's position (many of whom wouldn't know it.)  Rare events DO happen--it's not really fair to only notice and question them AFTER the fact.
Note--pregnancy in 1970 usually didn't involve the level of medical intervention (ultrasound, inducement of labor, etc.) it often gets now.