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Frequency tables, pie charts and stem and leaf diagrams
1.) Continuous data can be sorted into a frequency table. The class
intervals must not have gaps in between them or overlap each other.
2.) All possible values that round to the same number must fit into the same class
3.) Intervals do not need to be of equal width. Use narrower intervals where the
data is grouped together and wider intervals where the data is spread out.
4.) Pie charts can be used to show continuous data. The area of each sector
represents the frequency for that class interval. Other than this the chart is drawn
the same way as for discrete data.
Cumulative frequency diagrams
5.) If there are not too many observations they can be treated as individual
numbers and shown as a stem and leaf diagram. The stem shows the first
digit(s) of the numbers and the leaves show the last digit.
6.) Cumulative frequency is a running total of frequencies.
7.) Cumulative frequency diagrams can be used to estimate or predict other
Histograms and frequency polygons
8.) A histogram is similar to a bar chart but, because the data is continuous,
there are no gaps between the bars.
9.) A frequency polygon joins the midpoints of the top of the bars with straight
10.) A histogram shows how the data is distributed across the class intervals.
11.) A distribution can be symmetrical, have positive skew or negative
12.) To draw a histogram for unequal class intervals you need to adjust the
heights of the bars so the area is proportional to the frequency.
13.) The height of the bar, called the frequency density, is found by dividing
the frequency by the class width.
14.) The frequency density and the width of the class interval are used to work
out the frequency of each class interval in a histogram.
Frequency = Frequency Density X Class Width
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15.) Population pyramids look similar to two backtoback histograms. They
make it easy to compare aspects of a population, often by gender.
16.) They usually have class sizes, and therefore bars, the same width.
17.) A chloropleth map is used to classify regions of a geographical area.
Regions are shaded with an increasing depth of colour. A key shows what each
shade represents.…read more