|| Login  
Brandser, Berbaum, Dorfman et al. (2000)

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

Brandser EA, Berbaum KS, Dorfman DD, Braksiek RJ, El-Khoury GY, Saltzman CL, Marsh JL, Clark WA. Contribution of individual projections alone and in combination for radiographic detection of ankle fractures. American Journal of Roentgenology 2000;174:1691-1697.

Conclusion: The results for interpretation of single views show a clear superiority of the lateral view over the anteroposterior and mortise views for the detection of fractures of the posterior malleolus.

Readers: 4 (2 skeletal radiologists, 2 orthopedic surgeons)

Cases: 174 ankles: 34 fractures of posterior malleolus, 140 normals.

 

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

Conditions: (1) anteroposterior view alone, (2) mortise view alone, (3) lateral view alone.

Model = CBM, Parameter = sensitivity at specificity = 0.9, sensitivities = 0.203, 0.263, 0.713, respectively.

Readers = 4, Cases = 174,

MS( Treatment*Reader ) = 1.78362961,

MS( Treatment*Case ) = 1.45560223,

MS( Treatment*Reader *Case ) = 0.84380409.

 

Sensitivity Difference = 0.05

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

.

.

.

4

.

.

.

5

.

.

.

6

.

1846

.

7

.

1720

.

8

.

1625

.

9

.

1552

.

10

.

1493

.

11

.

1444

.

12

.

1404

.

13

.

1370

.

14

.

1341

.

15

.

1316

.

Note: Cells containing a period indicate that more than 2000 cases would be required.

 

Sensitivity Difference = 0.10

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

.

684

.

4

.

574

.

5

.

507

.

6

.

463

.

7

.

432

.

8

.

408

.

9

.

390

.

10

.

375

.

11

.

363

.

12

.

353

908

13

1402

344

537

14

1079

337

381

15

899

331

296

 

Sensitivity Difference = 0.20

Readers

Readers

and Cases

Random

Cases

Random

Readers

Random

3

.

173

.

4

.

145

.

5

469

129

506

6

252

118

196

7

189

110

122

8

158

104

89

9

140

99

70

10

127

96

58

11

118

93

49

12

111

90

43

13

106

88

38

14

102

86

34

15

98

85

31

 

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.

 


   Terms of Use   ||   Privacy Statement   ||   Copyright 2006 Medical Image Perception Laboratory