See How Grouping Changes Regional Summaries - Practice 1

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Combining small areas can change reported regional averages even when no underlying observations change. Always record the grouping rule. In these fictional equal-population zones, a two-zone regional rate is the arithmetic mean of the two zone rates.

Worked example

Two equal-population zones with rates 20% and 60% combine to 40%. Pairing the first with a 30% zone instead gives 25%.

Three equal-population zones have rates A 20%, B 40%, C 60%. Combining A and B gives 30%, while combining A and C gives 40%. Different groupings change the summary, not the underlying zone values.

Question 1 Three equal-population zones have rates A 10%, B 30%, C 50%. If a boundary groups A with C, what is that combined percentage? Answer

Question 2 Three equal-population zones have rates A 12%, B 32%, C 52%. If a boundary groups A with C, what is that combined percentage? Answer

Question 3 Three equal-population zones have rates A 14%, B 34%, C 54%. If a boundary groups A with C, what is that combined percentage? Answer

Question 4 Three equal-population zones have rates A 16%, B 36%, C 56%. If a boundary groups A with C, what is that combined percentage? Answer

Question 5 Three equal-population zones have rates A 18%, B 38%, C 58%. If a boundary groups A with C, what is that combined percentage? Answer