# Statistics: Standard Deviation, Random Chance and Unusual Results

[2] Neuroblastoma, a rare form of malignant tumor, occurs in 11 children in a million, so its probability is 0.000011. Four cases of neuroblastoma occurred in Oak Park, Illinois, which had 12,429 children.

a. Assuming that neuroblastoma occurs as usual, find the mean and standard deviation of cases in groups of 12,429 children.

b. Find the probability that the number of neuroblastoma cases in a group of 12,429 children is 0 or 1.

c. Does the cluster of four cases in Oak Park, Illinois, appear to be attributable to random chance? Why or why not?

[4] A recent Gallup poll consisted of 1012 randomly selected adults who were asked whether "cloning of humans should or should not be allowed." Results showed that 89% of those surveyed indicated that cloning should not be allowed.

a. If we assume that people are indifferent so that 50% believe that cloning of humans should not be allowed, find the mean and standard deviation for the numbers of people in groups of 1012 that can be expected to believe that such cloning should not be allowed.

b. Based on the preceding results, does the 89% result for the Gallup poll appear to be unusually higher than the assumed rate of 50%? Does it appear that an overwhelming majority of adults believe that cloning of humans should not be allowed?

#### Solution Preview

[2] Neuroblastoma, a rare form of malignant tumor, occurs in 11 children in a million, so its probability is 0.000011. Four cases of neuroblastoma occurred in Oak Park, Illinois, which had 12,429 children.

a. Assuming that neuroblastoma occurs as usual, find the mean and standard deviation of cases in groups of 12,429 children.

Let X be the cases of neuroblastoma in groups of 12,429 children. Then X follows a binomial distribution with n=12429 and p=0.000011. So,

Mean = E(X) = np = 12429*0.000011= 0.1367

Standard deviation = sigma(X) = root of [np(1-p)] = root of [12429*0.000011*0.999989] = 0.3698

b. Find the ...

#### Solution Summary

Standard deviation, random change and unusual results are examined.