| 1.4 | Frequency Histograms |
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- Key Idea 1: A histogram (also called frequency histogram) is a form of bar graph...
- The horizontal axis tells the scale of the observations.
- The vertical axis gives the number of data points, or frequencies, of the observations in various intervals.
Discussion
- Key Idea 2: An example – tar in cigarettes...
Discussion Step 1 - here are the raw data
1.1 4.0 4.5 4.9 7.2 7.5 7.9 8.3 8.9 9.0 11.6 12.1 12.5 12.9 13.3 14.1 14.7 15.0 15.0 15.3 15.8 16.2 16.8 17.3 Step 2 - put these data into a frequency table
Table Frequency Table of Tar (mg) per Cigarette
Interval Frequency (f) 0-2.5- 1 2.5-5.0- 3 5.0-7.5- 1 7.5-10.0- 5 10.0-12.5- 2 12.5-15.0- 5 15.0-17.5- 7 Total 24 Step 3 - here is the histogram
- X-axis intervals should all be the same width.
- You can experiment with different interval widths.
- More intervals shows more detail.
- Too many short intervals, though, let accidental variation hide the general shape of the data.
- In the histograms shown here, the x-axis labels are the interval boundaries; you can also label the interval mid-points instead.
- See an example of how a histogram relates to a stem-and-leaf plot.
| Discussion |
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