A procedure has a 2SD variation from a mean value. How many values from a normal population will 2SD include?

The correct answer is that 2 standard deviations (2SD) from the mean in a normal distribution includes approximately 95.45% of the values. This is a fundamental concept in statistics known as the empirical rule or the 68-95-99.7 rule, which describes how data is distributed in a normal distribution.

According to the empirical rule:

• About 68.27% of the data falls within 1 standard deviation (1SD) of the mean.

• About 95.45% of the data falls within 2 standard deviations (2SD) of the mean.

• About 99.73% of the data falls within 3 standard deviations (3SD) of the mean.

Thus, when considering a normal population and examining the range that extends 2 standard deviations above and below the mean, approximately 95.45% of the data points will fall within this range. This information is critical in fields such as medical technology and quality control, as it helps professionals understand and interpret variability and distributions of measurements accurately.