IPA IP 2021 Question 40
A question IPA Japan published in 令和3年度 ITパスポート試験 公開問題 問40, translated into English. ITPEC is based on the same exams.
In quality control in the test process of software that consists of multiple programs of the same level of difficulty, the number of bugs per unit number of steps of each program is graphed, and the programs that exceed the upper or lower limit line are to be detected as abnormal programs. Which of the following is the most appropriate diagram to be created?
Explanation
Control chart — plotting each program's bug density between an upper and a lower control limit picks out the programs that fall outside them.
A control chart plots a quality value for each sample, here the number of bugs per unit number of steps of each program, with a centre line at the mean and an upper and a lower control limit (commonly the mean ± 3 standard deviations). Because the programs are of the same difficulty, their bug densities should scatter around one mean; a point outside the limits signals a special cause. Above the upper limit the program is of poor quality; below the lower limit its testing may be insufficient. Both are treated as abnormal.
Answer (a)
Why not others:
- •(b) — a cause and effect (fishbone) diagram arranges the causes behind one quality problem as branches; it has no values and no limit lines
- •(c) — a Pareto chart sorts categories by frequency in descending bars with a cumulative line, to decide which to tackle first; it has no limits
- •(d) — a radar chart plots several evaluation items on axes radiating from a centre, to show the balance of one subject across the items
Key rule: Upper and lower limit lines around a centre line mark a control chart, the QC tool for spotting abnormal values in a series of samples.
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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.