A survey’s margin of error gives a range of plausible percentages for the whole population. For the highest estimated count, add the margin in percentage points to the reported percent, then use Desmos’s % of to apply that upper percent to the population. The trap is treating percentage points as a percent change or applying the result to the sample instead of the whole county.
Hints
- Hint 1
The margin of error tells you how far the county’s support percentage might be from the reported estimate. To find the highest plausible percentage, should you add or subtract the given number of percentage points?
- Hint 2
After finding the upper percentage, apply it to all registered voters in the county, not the people surveyed. In Desmos, which number should go after
% of?
Step-by-step
Use the upper end of the estimate
Step 1Find the highest plausible percentage
The reported estimates support among all registered voters. A margin of error of percentage points means the highest plausible percentage is points above that estimate. Add the points directly:
Percentage points add to the reported percent; they aren’t of that percent.
- Step 2
Turn the percentage into a countywide count
Use the whole county, not the -person sample, as the base. Type in Desmos; it displays . So the highest estimated number of registered voters who might support the increase is . Grid in 70800.