5.9 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 5.3.

TABLE 5.3: 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

Explain whether the study is observational or experimental (true or quasi).
What would be the meaning of column percentages for this table?
What would be the meaning of row percentages for this table?
Would row or column percentages probably be more sensible to use? Why?
Compute the percentage of residents in the sample overall not detecting the odour at all.

References

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.