Transcript 09/03/2015

Psychology 202a
Advanced 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)