ITPEC FE Morning April 2023 Question 78
There are several quality control tools that are used primarily for manufacturing and inspection departments. Which of the following is a graph where appropriate units or attributes for the data are set on the vertical and horizontal axes correspondingly and measured values are plotted accordingly?
Explanation
Scatter diagram — two characteristics on the two axes and one point per measurement, to see whether they are correlated.
Each item measured gives a pair of values, one read on the horizontal axis and one on the vertical, and is plotted as a point. If the points rise together, fall together or form no pattern, the two characteristics are positively correlated, negatively correlated or unrelated, for example oven temperature against defect rate.
Answer (d)
Why not others:
- •(a) Control chart — plots one characteristic in time order with a centre line and control limits, to detect when a process goes out of control
- •(b) Histogram — bars showing how often the values of one characteristic fall in each interval, the shape of its distribution
- •(c) Pareto chart — bars for items in descending order of frequency or cost with a cumulative-percentage line, to find the vital few problems
Key rule: A scatter diagram relates two variables; a histogram shows the distribution of one, a control chart follows one over time, and a Pareto chart ranks categories.
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