Math 151, Day 9, Friday, Feb. 16, 2001
final version
More help: Mary Moscowitz, who assisted Math 151 last year, is in
the Math Clinic 7-9 Monday evenings.
Hour exam, a week from today (Day 12).
Covers thru Monday's assignment.
Homework notes: Just because SPSS will do some of your
work, don't abdicate responsibility. You still have to label your
graphs, tell what you're counting or measuring. Make conclusions if any.
And if you have a bunch of output and the desired answers are in there
someplace, you have to find them and mark them for your reader/self.
Since they are printed on paper, and you all own pens or pencils, this
is not too onerous.
Normal area problems, Day 8
"Backward problems" "What
raw (x) value has area ___ to the left/right
of it?"
Sketch the curve, labeled with x values and z values, and the
Area, roughly.
Restate
(if
needed) as "What z value has area A to the LEFT of it."
Look
in body of table for the value closest to A.
Go
to edge(s) of table to find what z that goes with.
Convert
the z to an x:
z is the number of standard deviations above the mean.
Multiply z by the size of 1 standard
deviation. Now you have distance above
the mean, measured in raw units.
Add the mean.
Now you have the "raw" value x.
Example: Whatx
value
has 10% of the observations above it? This is the same
x as the one for:
What
x value has 90% of the observations below
(to the left of) it.
The table gives z = 1.28, approximately. The Wechsler score x=
mean
+ z (s.d.) = 110
+ 1.28 (25) = 142
Percentiles: a Wechsler score of 142
has 90% of the scores at or below it. 142 is the 90th percentile.
Read on your own:
discussion Monday
Related quantitative variables (scatterplots) (Ch. 2)
"Just Related" or "explanatory & response?"
explanatory = independent = "x"
= horizontal axis ( = "cause", sometimes but
not always)
response = dependent=
"y" = vertical axis
= ("effect ")
Discussing Scatterplot
General Pattern
Deviations
Clusters?
Outliers?
Shape (linear, curved, ...?)
Strength of relationship (how unfuzzy)
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)
Handout: Supplement to SPSS manual,
for pp. 62-71: SPSS for BPS Chapter 2--Plotting Relationships
HW Day 9, Friday Feb 16. (Re)read
pp. 61-64, using the table "backward". Summary, pp. 66-69.
Read Ch. 2 (Examining relationships), pp. 78-91. Read ahead,
2.2 (correlation)
Hand in Monday, as Day
9
*Problems assigned last time.
"Backward Normal"Always sketch a normal curve
first,
roughly mark the proportion=area you are given.
p. 76 1.89 (soldiers' heads)
p.64 1.68 c (pregnancy)
p. 66 1.70 (z-scores of quartiles)
Hand in Wednesday, with Day 10
Relationships & Scatterplots:
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
2.10 states'mean/median income
2.14 (SPSS) (teachers' pay vs.no HS) |
Read, to discuss
|
Optional (more practice)
"Backward"
p. 62 1.60 (WAIS)
+Learn to use SPSS to find
the values-- manual pp.58-59:"IDF"
|
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