1. Explain how it might happen that the true population mean would not fall within a confidence interval created to estimate the mean.
2. When opinion polls are reported in the press, they given an error of + 3 points for example. Explain what that + 3 means.
2006-10-05 06:52:49 · 2 answers · asked by oneluv804 2 in Science & Mathematics ➔ Mathematics
1. The trouble with the mean is that it can be skewed by outlying values. This is how it can fall outside a confidence interval.
2. Actually, they should say + or - 3 points. It means that the number they report (for example, a 50% approval rating) can be off by 3 percentage points either way, so the true opinion of the entire population is likely to fall somewhere in the range of 47-53%.
2006-10-05 07:08:09 · answer #1 · answered by James L 5 · 0⤊ 0⤋
Another reason for 1 is that, for a 95% confidence interval, the mean falls in the interval 95% of the time that you sample and calculate it. Thus, 5% of the time, the confidence interval does NOT capture the mean.
Another reason could be that you don't have a random sample, but one that is biased in some way.
2006-10-05 13:20:34 · answer #2 · answered by tehabwa 7 · 0⤊ 0⤋