MATH 251, Probability and Statistics I, Fall 2001, Day 2
Handout: Stemplot (stem and leaf) invented by John Tukey
Not in text:
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.)
Dotplot: Note bottom of p. 52, fig.
1.17, use of a to display a data set of size n
= 7. Just put a dot for every observation at its numerical place
on the axis. Stack them up if needed.
WHICH?
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.
Unless otherwise noted, all assignments are in Moore & McCabe,
Intro to the Practice of Statistics, 3rd ed. ("IPS")
Italics are notes to myself--which problem is it?
Day 2 (Mon. Sept 3) Assigned:
(Re) Read: Introduction. Section 1.1. Read
ahead, 1.2 thru p. 51.
Do to hand in:
1.22, 1.28 (stem)
1.39, 1.40 (time) |
Read, be prepared to discuss
1.27
1.35, 1.36 |
Optional |
Begin (will be assigned to hand in later)
1.53, 1.42, 1.43 (a-d)
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