Testes de Bioestatística
1. In general, which of the following statements is FALSE?
(a) The sample mean is more sensitive to extreme values than the median.
(b) The sample range is more sensitive to extreme values than the standard deviation.
(c) The sample standard deviation is a measure of spread around the sample mean.
(d) The sample standard deviation is a measure of central tendency around the median.
(e) If a distribution is symmetric, then the mean will be equal to the median.
Solution: d
2. A sample of 99 distances has a mean of 24 feet and a median of 24.5 feet. Unfortunately, it
has just been discovered that an observation which was erroneously recorded as “30” actually
had a value of “35”. If we make this correction to the data, then:
(a) the mean remains the same, but the median is increased
(b) the mean and median remain the same
(c) the median remains the same, but the mean is increased
(d) the mean and median are both increased
(e) we do not know how the mean and median are affected without further calculations; but the
variance is increased.
Solution: c
3. A researcher is studying the hatching Yellow Bellied Sapsuckers. She has a study group of 40
eggs. A similar study has shown that the eggs’ hatching times should have a mean of 42 days
and a variance of 9 days (note that variance is (std dev) 2). Her thesis advisor has suggested that
the distribution of hatching times will have the same shape as that of the Purple Throated Tree-
tappers, which is “mound shaped”. If the researcher is willing to assume that her advisor is
correct, how may eggs will have hatching times between 36 and 48 days?
(a) Approximately 55%, or around 22 eggs.
(b) Approximately 68%, or around 27 eggs.
(c) Approximately 75%, or around 30 eggs.
(d) Approximately 95%, or around 38 eggs.
(e) Almost all of the eggs.
Solution: d
4. The distribution of the heights of students in a large class is roughly bell shaped. Moreover,
the average height is 68 inches, and approximately 95% of the heights are between 62 and 74
inches. Thus, the standard deviation of the height distribution is approximately equal to:
(a) 2
(b) 3
(c) 6
(d) 9
(e) 12
Solution: b
5. The average time between infection with the AIDS virus and developing AIDS has been
estimated to be 8 years with a standard deviation of about 2 years. Approximately what fraction
of people develops AIDS within 4 years of infection?
