Part 3: Statistics: concepts and problems

1.      To achieve an estimated percent standard deviation of 2%, _______ counts must be collected.

 

a)   400

b)   1,414

c)   2,500

d)   10,000

 

2.      A measurement is made in which 2,500 counts are collected. There is a 95.5% probability that repeated measurements will yield between ______ and ______  counts.

 

a)   2,400; 2,500

b)   2,400; 2,600

c)   2,450; 2,500

d)   2,450; 2,550

e)   2,500; 2,555

 

3.      Answer True/False to the following statements:

 

a)   reliability depends upon agreement of observed value with true or actual value

b)   reliability depends upon reproducibility of measured values

c)   precision is a measure of both reliability and accuracy

d)   accuracy is a measure of both reliability and precision

e)   accuracy relates to agreement of observed and true values

 

4.      The following series of measurements was made: 11, 10, 10, 11, 10.5. The standard deviation for these measurements using an (N-l) weighting is:

 

a)    0.25

b)    0.50

c)    0.20

d)    0.447

 

  5. Which of the following tests are performed periodically on a radioisotope dose calibrator?

 

a)    accuracy, precision, constancy

b)    precision, reliability, constancy

c)    accuracy, constancy, reliability

d)    accuracy, constancy, linearity

e)    accuracy, precision, linearity

 

 6. Consider the statistics formulae and statements below: mark each True or False

 

a)   the mean value of a series of numbers = SX_i/n where n= number of values

b)   the mean value of a series of measurements always equals the median value

c)   the standard deviation is represented by the 

formula

                              s = ±  V   S (X_i-X)²
                                                          (N-1)

 

d)   the curve at right is skewed to the left.

 

   s  of the mean

f)    The lower the number of c², the better the correlation between expected and measured values

g)   “mean ± 2s “is used to set the normal range for lab values

 

   7.   A radioactive sample yields 81 counts (including background). A background count of the same duration yields 64 counts. The standard deviation of the difference between these counts is approximately:

 

a.   4

b.   8

c.   9

d.   12

 

   8.   A three minute observation is made from which the count rate is found to be 300 counts per minute. The standard deviation of this count rate is:

 

a. 30

b. 14

c. 17.3

d. 10

e. 9