After measuring the length and width of the block last week, you were asked the following question: "Since your measurements of the length and width are subject to random error, how should you report the area of the block including a 90% confidence interval?" Remember what we mean by "confidence interval". We expect the mean of a small number of measurements, plus or minus one standard error, to overlap the true mean approximately 6 times out of 10. Thus, an interval equal to +/- the standard error in our measurements is referred to as a 60% confidence interval. Similarly, an interval of +/- 2 times the standard error in our measurements is referred to as a 90% confidence interval.