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Franken, Berbaum, Marley et al. (1992)

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

Franken EA, Berbaum KS, Marley SM, Smith WL, Sato Y, Kao SCS, Milam SG. Evaluation of a digital workstation for interpreting neonatal examinations - A receiver operating characteristic study. Investigative Radiology 1992;27:732-737.

Readers: 4 pediatric radiologists

Cases: 100 neonatal intensive care patients, 67 with abnormalities

Cases: 67 neonatal intensive care patients with subtle abnormalities, 33 neonatal intensive care patients without abnormalities (100)

Rating: probability of abnormality on a 5-point scale (1=definite abnormality)

Conditions: (1) Digital display of digitized plain film images. (Also referred to as PACS Display (Picture Archiving and Communications System.) [PACS], (2) Plain film display. [PF]

 

ROC Model = propROC, Parameter = AUC,

AUCs = 0.870, 0.853, respectively.

Readers = 4, Cases = 100,

MS( Treatment*Reader ) = 0.00327658,

MS( Treatment*Case ) = 0.07242917,

MS( Treatment*Reader *Case ) = 0.07854222.

AUC Difference = 0.03

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

99

459

99

4

93

345

93

5

87

276

87

6

81

231

81

7

77

198

77

8

73

174

73

9

69

155

69

10

66

139

66

11

63

127

63

12

60

117

60

13

57

108

57

14

55

100

55

15

53

94

53

 

 

 

 

AUC Difference = 0.05

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

91

167

91

4

77

126

77

5

66

101

66

6

58

85

58

7

52

73

52

8

47

64

47

9

43

57

43

10

40

52

40

11

37

47

37

12

34

44

34

13

32

40

32

14

30

38

30

15

28

35

28

 

 

AUC Difference = 0.10

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

65

44

65

4

43

33

43

5

32

27

32

6

25

23

25

7

21

20

21

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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