Confidence Interval examples 1 While performing a task under simulated weightlessness the pulse rate of 12 astronauts increased an average of 27 33 beats per minute with a standard deviation of 4 28 beats per minute Construct a 99 confidence interval for the true average increase in pulse rate of the astronauts 2 At eight different locations paint used to mark crosswalks deteriorated after being driven over by several million cars For the eight locations the mean number of cars that would cause deterioration was 14 10 and their standard deviation was 1 67 million car crossings Calculate a 95 confidence interval for the true mean of the population sampled