Question

To study bonding between mothers and infants, a researcher places each mother and her infant in a playroom and has the mother leave for 10 minutes. The researcher records crying time in the sample of infants during this time that the mother was not present and finds that crying time is normally distributed with M = 5 and SD = 1.4. Based on the empirical rule, state the range of crying times within 68% of infants cried, 95% of infants cried, and 99.7% of infants cried. (a) 68% of infants cried to min (b) 95% of infants cried to min (c) 99.7% of infants cried to min

Answer 1

The distribution given here is with mean = 5 and standard deviation = 1.4

a) According to the empirical rule, 68% of the observations must lie within one standard deviation from the mean.

Therefore it means they should lie from 3.6 minutes to 6.4 minutes.

b) According to the empirical rule, 95% of the observations must lie within two standard deviations from the mean.

Therefore it means they should lie from 2.2 minutes to 7.8 minutes.

c) According to the empirical rule, 99.7% of the observations must lie within three standard deviations from the mean.

Therefore it means they should lie from 0.8 minutes to 9.2 minutes.