Although newspapers frequently report survey results, they typically do not use confidence intervals.  Instead, they will report the population mean with a plus/minus amount of error (e. g. 25% ± 2%).  For the following survey information, convert the “plus/minus” language into a confidence interval, and then, using the “Confidence Intervals for Population Proportion” spreadsheet, approximate the value of the level of confidence, c, for each situation.  In a survey of 8451 U. S. adults, 31.4% said they were taking vitamin E as a supplement.  The survey’s margin of error is plus or minus 1%.

In a survey of 1001 U. S. adults, 27% said they had smoked a cigarette in the past week.  The survey’s margin of error is plus or minus 3%.

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