Psychology 202aAdvanced Psychological

Statistics

September 3, 2015

The show so far

• Last time we talked about:– variables– distributions– grouping– ways of understanding the shape of a

distribution

Peabody Distribution

Values Frequency

55 – 59 1

60 – 64 2

65 – 69 5

70 – 74 2

75 – 79 4

80 – 84 8

85 – 89 6

90 – 94 8

95 – 99 3

100 – 104 1

Software

• We saw that functions in R tend to use fairly intuitive names (e.g., sort(), stem()).

• We were about to introduce SAS and begin a discussion of descriptive statistics. Let’s do that now.

Ways of understanding shape

• Graphics.

• Descriptive statistics.

Histograms

• A histogram is a picture of the frequency distribution:– group the data (7 to 15 intervals)– identify real limits and midpoints of intervals– draw “histobars” over the intervals– use informative labels

Peabody Distribution

Values Frequency

55 – 59 1

60 – 64 2

65 – 69 5

70 – 74 2

75 – 79 4

80 – 84 8

85 – 89 6

90 – 94 8

95 – 99 3

100 – 104 1

Histograms in R

• hist(Peabody)

• R has done a pretty good job:– informative labels– reasonable number of intervals

• but the limits R chose for the intervals are a little strange

• help(hist)