Answer
True positive = 780
True negative = 160 − 15 = 145
False negative = 840 − 780 = 60
False positive = 15
Questions
- Define accuracy and precision.
- Do systematic errors give an accurate measurement? Can systematic
errors give a precise measurement? - A radioactive sample gives 15,360 counts in 9 min:
(a) What are the count rate of the sample and its standard deviation?
(b) If the sample contained a background count rate of 60 cpm obtained
from a 2-min count, what would be the net count rate of the sample
and its standard deviation? - How many counts of a sample are to be collected to have a 1% error at
the 95% comfidence level? - Within how many standard deviations of a mean count of 62,001 is 730?
- To achieve an estimated percent standard error of 3%, how many counts
must be collected? - The c^2 value of 11 measurements of a quantity is 4.2. What is the prob-
ability that the variations of measurements are due to statistical varia-
tions of the quantity?
Suggested Readings
Bahn AK.Basic Medical Statistics.New York: Grune & Stratton; 1972.
Martin PM. Nuclear medicine statistics. In: Rollo FD, ed.Nuclear Medicine Physics,
Instrumentation and Agents.St. Louis: Mosby; 1977:479–512.
Negative predictive value =
+
=×=
145
145 60
145
205
100 70 7.%
Positive predictive value =
+
=×=
780
780 15
780
795
100 98 1.%
Accuracy=
+
+++
=×=
780 145
780 145 60 15
925
1000
100 92 5.%
Specificity=
+
=×=
145
145 15
145
160
100 90 6.%
Sensitivity=
+
=×=
780
780 60
780
840
100 92 6.%
Suggested Readings 43