Theory question 302
Statistical Maps and DiagramsThe Table C below shows the value of imported commodities by a country in the years 2016 to 2020. Study and use it to answer the questions that follow.
Table C (value of imported commodities in million Naira)
2016: 80
2017: 120
2018: 240
2019: 60
2020: 300
(a) Using a vertical scale of 2 cm to represent 40 million units of the value of imported commodities, construct a divergent bar graph to represent the data (b) State two disadvantages of divergent bar graphs.
Show the model answer
(a) Mean = (80 + 120 + 240 + 60 + 300) ÷ 5 = 800 ÷ 5 = 160 million. Deviations: 2016 −80; 2017 −40; 2018 +80; 2019 −100; 2020 +140. Draw a horizontal base line for the mean (160); bars above for 2018 (4 cm) and 2020 (7 cm) and below for 2016 (4 cm), 2017 (2 cm) and 2019 (5 cm); equal widths, labelled years, axis, title and key.
(b) The actual values are not shown directly; calculating the mean and deviations takes time; difficult to read exact values; not suitable for many items; the base (mean) changes with the data, so graphs are hard to compare.
Work out the mean first.