MATH 251, Probability and Statistics I, Fall 2005, Mon. Aug. 29, Day 2 TA hours changedHit reload for most current version

Day 2 (Mon. Aug. 29) Assigned:
   (Re) Read:   Section 1.1, rest of.  Postpone timeplots till we do SPSS.  Read ahead, 1.2 thru p. 49.

Do to hand in: p. 25ff. 1.22  Make a stemplot (no histogram) & answer a,b 1.23  Use the applet (help here).  Find the dataset under the DataSets tab, then click the histogram tab. 1.37 all: Truncate, don't round.  Easiest to do (d) first and then combine for b.  (Don't bother to order them.) 1.38 Studytime--back to back 1.24  CO2 Use stemplot.  Use stems 0,1,2,...(2|3 = 2.3) or 0*, 0t, 0f... (0|2 = 2, 1|9 = 19) 1.17 Make a dotplot, not a stem.

Read, be prepared to discuss  p. 94, 1.128 (leisure time) p. 29, 1.15, 1.16

Optional

LaReina's hours: T 7-9 pm, W 10am-12n, Th 1-3
Distribution of one variable:  what values, how many (or what proportion) of each.
        "Make Piles" -- Frequency table:  count,  percent="relative frequency"  (Hair color)

Graphical summaries of data:  Area represents proportion.
    Categorical: Bar or pie graph  (Bar chart ordered by size = "Pareto chart")
             Pie only ok if showing all categories (part of whole) & no overlap of categories.
                Pie by hand?  Template handout
    Quantitative: Histogram.  Stem-and-leaf (Stemplot). Dotplot
          Counts or proportions = heights; Equal width bars on continuous base ensures "Area represents proportion."
          Describing:  Pattern-- and deviations from it
          Shape (symmetric, or skewed (think smeared, or sliding) right or left),
              (Humps: uni- or bi- modal (multi-)   Two humps = two "causes"?  M+F heights)
               Some special shapes:  uniform (flat)   J-shaped (p. 36 top left) bell-shaped (sec. 2.3)
          Center, Spread (roughly now)
          Outliers,  gaps ? (different groups, sources?)
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 does also. Some sources 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.)  Don't put the leaves in order unless you need to--waste of time.

Dotplot: Note bottom of p. 50, fig. 1.19, use of a dot plot 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.