Margin of error

[mattc]

When opinion polls are reported in the press, they are given a margin of error, for example, of ±3 points. Explain what that ±3 means now that you've learned about confidence interval estimation.

[omega]

±3 gives half the width of the confidence interval. It indicates that the true value is within 3 points away from the statistic obtained from the survey (usually the sample mean or proportion).