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Krupinski, Gonzales, Gonzales, & Weinstein (2000)

Reader and case sample combinations needed for 0.80 power based on the data of:

Krupinski E, Gonzales M, Gonzales C, Weinstein RS. Evaluation of a digital camera for acquiring radiographic images for telemedicine applications. Telemedicine Journal and E-Health 2000;6:297-302.

Goal: to determine if a digital camera and a light box could be used at rural telemedicine sites to acquire and transmit reproductions of radiographic images for evaluation by a radiology or orthopedic specialist at a telemedicine hub site in place of an x-ray digital scanning device.

Readers: 2 orthopedic surgeons and 2 radiologists

Cases: 40 cases, 16 were lesion free/normal; 13 with subtle fracture; 5 with significant sprain; 4 with osteoarthritis, osteoporosis, or degenerative joint disease; 2 with foreign bodies.

Rating: Provide a diagnosis and report confidence in it using a 6-point scale.

Conditions: (1) original film images vs. (2) digital camera photographs of plain film radiographs viewed on a color monitor.

ROC Model = propROC, Parameter = AUC,

AUCs = 0.947, 0.925, respectively.

Readers = 4, Cases = 40,

MS( Treatment*Reader ) = 0.00711334,

MS( Treatment*Case ) = 0.03884468,

MS( Treatment*Reader *Case ) = 0.04340888.

 

AUC Difference = 0.03

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

46

255

46

4

44

192

44

5

41

154

41

6

39

129

39

7

37

111

37

8

35

97

35

9

34

87

34

10

32

78

32

11

31

71

31

12

30

66

30

13

29

61

29

14

28

57

28

15

27

53

27

 

 

AUC Difference = 0.05

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

43

93

43

4

37

71

37

5

33

57

33

6

29

48

29

7

26

41

26

8

24

37

24

9

22

33

22

10

21

30

21

11

20

27

20

12

20

25

20

13

20

23

20

14

20

22

20

15

20

21

20

 

 

AUC Difference = 0.10

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

32

25

32

4

22

20

22

5

20

20

20

6

20

20

20

7

20

20

20

8

20

20

20

9

20

20

20

10

20

20

20

11

20

20

20

12

20

20

20

13

20

20

20

14

20

20

20

15

20

20

20

 

Cautionary note:  For this data set the estimated required number of cases when only cases are treated as random sometimes considerably exceeds the required number when both cases and readers are treated as random. If the variance components were all known, this would not be possible. It happens here because we are using unbiased estimates of the variance components rather than the true unknown parameter values; in particular, it happens because the treatment-by-reader variance component estimate is negative.  In this situation a conservative approach is to rerun the program with the treatment-by-reader variance component estimate set to zero.  Alternatively, in this situation you may want to consider pooling information from several similar studies, resulting in more precise variance component estimates and hence more precise sample size estimates.  The reader is referred to the Details section of the MRMC Sample Size User's Guide for further information.

 


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