4.18 Optional: Percentages

This question is optional; for example, if you need more practice, or you are studying for the exam.

(Answers are available in Sect. A.5)

Industries often produce unpleasant odours, but the effects on the health of those impacted is not always clear.

Furthermore, different communities are impacted in different ways. One study (Deane and Sanders 1978) researched the RQ:

In Carson, California, does the odour from nearby petroleum refineries impact residents in different areas differently?

One aim of the study was to determine if the reports of unpleasant odours were related to measurements made by a dynamic olfactometer (an 'electronic nose'). Part of the data collected are shown in Table 4.5.

TABLE 4.5: Data on the impact of a local industry
Area I Area II Area III Total
At least once a week 48 48 16 112
Between once a week and once a month 23 21 10 54
Less often than once a month 14 14 20 48
Not at all 12 12 53 77
  1. Explain whether the study is observational or experimental (true or quasi).
  2. What would be the meaning of column percentages for this table?
  3. What would be the meaning of row percentages for this table?
  4. Would row or column percentages probably be more sensible to use? Why?
  5. Compute the percentage of residents in the sample overall not detecting the odour at all.


Deane M, Sanders G. Annoyance and health reactions to odor from refineries and other industries in Carson, California 1972. Environmental Research. 1978;15:119–32.