A series of bar charts

Sometimes data are collected annually (or at other regular intervals) that could be displayed as a bar or pie chart for each year. For example, the data could be a frequency table or other partition of some total quantity.

A series of clustered or stacked bar charts can show how the values change over time.

Recycling of aluminium cans

The following table was published to show sales and recycling of aluminium beverage in Australia between 1978 and 1989. Each year's data can be easily rewritten in the form of a frequency table as shown on the right below.

As published...   Frequency table...
  Cans (000)     Cans (000)  
 Year     Sold      Returned      Year    Returned     Unreturned   % ret
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
917
1290
1196
1360
1466
1393
1596
1577
1827
2037
2321
2523
165
297
550
680
733
752
816
820
950
1100
1300
1566
 
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
917
1290
1196
1360
1466
1393
1596
1577
1827
2037
2321
2523
752
993
646
680
733
641
780
757
877
937
1021
957
18
23
46
50
50
54
51
52
52
54
56
62

The next diagram shows the data graphically as a clustered bar chart in each year.

Firstly click the checkbox Stacked to display each year's cans as a stacked bar chart. The stack heights show the increase in the total number of aluminium cans sold each year over this period. The black bars also show the increase in the number of recycled cans.

Now choose Percent within Year from the pop-up menu. The stacked display now shows how the proportion of cans that were recycled increased.

The stacked bar charts of counts and proportions highlight different aspects of the data. The choice of which to use depends on the message you are trying to convey.