Basic Statistics

92 ESTIMATION OF POPULATION MEANS: CONFIDENCE INTERVALS

Give a 95% confidence interval for the difference between the mean weight of

male mice and female mice using a statistical program.

To study whether or not pressure exerted on the upper arm increases bleeding

time, 39 persons had their upper arm subjected to a pressure of 40 mmHg of

mercury and their fingers pricked. Their mean bleeding time was 2.192 min,

and the standard deviation of their bleeding times was .765 min. Forty-three

other persons acted as controls. No pressure was used for the controls, and

their bleeding time was found to have a mean of 1.524 minutes and a standard

deviation of .614min. Give a 95% confidence interval for the difference in

bleeding times. Do you think pressure increases mean bleeding time? Why?

7.5

7.6 (a) A special diet was given to^16 children and their gain in weight was recorded

over a 3-month period. Their mean gain in weight was found to be 2.49 kg. A

control group consisting of 16 children of similar background and physique

had normal meals during the same period and gained 2.05 kg on average.

Assume that the standard deviation for weight gains is .8 kg. Is the evidence

strong enough for us to assert that the special diet really promotes weight

gain?

(b) Answer the question in (a) if each of the two groups consisted of 50 children.

7.7 A general physician recorded the oral and rectal temperatures of nine consecu-

tive patients who made first visits to his office. The temperatures are given in

degrees Celsius ("C). The following measurements were recorded:

Patient Number Oral Temperature (deg"C) Rectal Temperature (deg"C)

37.0

37.4

38.0

37.3

38.1

37.1

37.6

37.9

38.0

37.3

37.8

39.3

38.2

38.4

37.3

37.8

37.9

38.3

(a) From this data, what is your best point estimate of mean difference between

oral and rectal temperatures?

(b) Give a 95% confidence interval for this difference, and state what the interval

means.

(c) Give a 95% confidence interval for mean oral temperature.

(d) Give a 95% confidence interval for mean rectal temperature.