Math 151 , Spring 2001, Day 2 Hit reload to
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final version
Continuing graphical summaries of data:
Area represents proportion.
Distribution of one variable: what
values, how many (or what proportion) of each.
Quantitative:
Histogram (computer)
or Stemplot (Stem-and-leaf) (by hand)(or dot plot, see below)
I
will only require you to read, not make histograms by hand..
Stemplots
are a powerful hand tool.
Unordered first, then ordered if necessary. By tens, then split?
Back to back, comparing two groups.
Describing: Pattern-- and deviations
from it
Shape (symmetric, skewed (think smeared) right or left), center,
spread--outliers?
Bimodal= two humps. Two causes, two classes?
What do we see? What can we infer?
Data source? Lurking variables?
Variability happens.
Things settle down on average, BUT conclusions are never certain.
Statistics gives us a language
for talking about uncertainty.
Choosing a display (by hand): Note bottom of p. 38, fig.
1.12, use of a to display a data set of size n
= 7.
A dot plot is
most useful for n = 3 to about 15-20, or when the data only fall on a few
values (just stack the dots up).
A stemplot is
good for continuous data, smeared around; you can do 100 values in 3-5
minutes.
Day 2(Wed. Jan. 31): Reading: Section 1.1, + stemplot
handout, Ahead in 1.2 thru p. 37.
Italicized notes give me a hint which problem it is. [my comments]
Problems on the same line usually cover similar
issues.
NOT covered in class--Needed for HW:
Stemplot, rounding when there are more than
2 decimal places? Handout says truncate (round down), Moore
text says round to nearest. Tukey, the inventor, said truncate;
throw away the trailing digits; I agree. This is supposed to be fast--rounding
to nearest slows it down. I encourage truncating but you can do it
either way and be right. If you truncate, your stemplot may look
a little different from the text answers. (A stemplot is
hard for a computer to do, but some packages do. For them, rounding to
nearest is easiest. SPSS truncates, which is hard for a computer.)
Hand in .
p. 20, 1.14 (hurricane hist)
1.17 (cf. age dist.)
p. 17 1.9 (stem: SSHA)
p. 22ff, 1.18 &19 (back to back HR)
1.24 (pop
of states) |
Read, to discuss
1.15 batting, 1.16 coins
|
Optional
1.26 teachers' salaries |
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