問15
頻出度★★★
クラスの学生の8科目の成績をそれぞれ5段階で評価した。クラスの平均点と学生の成績の比較や，科目間の成績のバランスを評価するために用いるグラフとして，最も適切なものはどれか。
平成25年度 秋期 ITパスポート試験 問15
ストラテジ系企業活動 › 業務分析・データ利活用
This question's explanation and your answers so far.
解説
問 15
Incorrectア
A pie chart treats the whole circle as 100% and uses the area of each sector to show the composition ratio (breakdown) of each item. It is meant for looking at each part's share of a total, so lining up values whose total has no meaning — such as 5-level ratings for 8 subjects — produces a composition ratio that is meaningless. Also, one circle can represent only one data series, so the class average and the student's grades cannot be overlaid and compared. Nor can you read off whether the balance is good or bad.
Incorrectイ
A scatter plot takes two quantities as the horizontal and vertical axes, plots points, and examines the correlation (the strength of the relationship) between the two variables from how the points are scattered. Because it has only two axes, it cannot line up as many evaluation items as 8 subjects at the same time, and it is not suited to showing the balance among subjects as a shape. It is a chart for correlation analysis, and it cannot be used to compare against an average or to evaluate how balanced things are.
Incorrectウ
A Pareto chart arranges items as bars in descending order of count or amount and overlays the cumulative ratio as a line. It is used in ABC analysis and the seven QC tools to find the small number of items that should be dealt with as priorities. Because the items are re-sorted in descending order, the ordering of the subjects is not fixed, so it does not work for evaluating balance. It is also not a chart whose purpose is to place an average alongside another data series for comparison.
- エ
正解 The correct answer is “エ Radar chart”. A radar chart draws as many axes radiating out from a center point as there are evaluation items, plots a value on each axis, connects those values with lines, and shows the overall picture through the shape of the resulting polygon. In this question the 8 subjects become 8 axes, and the 5-level rating becomes the scale on each axis. If the polygon is close to a regular polygon, the subjects are well balanced; if it is dented somewhere, you can intuitively read from the shape that this subject is a weak point. In addition, the polygon for the class average and the polygon for the student's own grades can be drawn overlaid on the same chart, so you can compare subject by subject at a glance which subjects are above the average and which are below it. The radar chart is the only chart that satisfies all three requirements of the question: multiple evaluation items, balance among the items, and comparison of multiple data series.
ここがポイント
- Radar chart = a chart that takes multiple (three or more) evaluation items as radiating axes and shows the balance among the items through the shape of a polygon. Since multiple data series can be drawn overlaid, it can also be used to compare an average with an individual's values.
- Choose a chart according to your purpose. Composition ratio → pie chart (100% stacked bar chart); correlation between two variables → scatter plot; narrowing down priority items (ABC analysis) → Pareto chart; comparing balance across many items → radar chart; change over time → line chart.
用語