Table IV.
Precision and accuracy: for the individualx, y and z coordinate axes for the RSA methods. True mean wear was 0.832 mm (0.01 to 4) for the x and y axes and -0.832 mm (-0.01 to -4) for the z axis (CI, confidence interval)
| Precision (n = 15 double measurements) | Accuracy (n = 14 mean double measurements) | ||||||
|---|---|---|---|---|---|---|---|
| Wear measurement method* | Bias (95% CI)* | Sr‡ | 95% repeatability limits§ | Mean (range)¶ | Bias (95% CI)** | RMSE†† | |
| EGS-RSA (mm) | |||||||
| x | -0.047 (-0.062 to -0.032) | 0.020 | 0.054 | 0.832 (0.020 to 3.975) | 0.000 (-0.026 to 0.026) | 0.046 | |
| y | -0.040 (-0.058 to -0.022) | 0.023 | 0.065 | 0.877 (0.058 to 4.130) | 0.045 ( 0.018 to 0.072) | 0.046 | |
| z | 0.090 (0.040 to 0.140) | 0.063 | 0.176 | -1.034 (-0.098 to -3.996) | -0.202 (-0.270 to -0.034) | 0.117 | |
| MB-RSA (mm) | |||||||
| x | -0.115 (-0.145 to -0.085) | 0.038 | 0.105 | 0.804 ( 0.070 to 3.941) | -0.028 (-0.061 to 0.005) | 0.056 | |
| y | -0.063 (-0.087 to -0.039) | 0.031 | 0.085 | 0.927 ( 0.103 to 4.180) | 0.095 ( 0.071 to 0.119) | 0.042 | |
| z | 0.135 (0.060 to 0.210) | 0.096 | 0.265 | -1.346 (-0.324 to -4.222) | -0.513 (-0.634 to -0.392) | 0.209 | |
* EGS-RSA, RSA method featuring analysis of head penetration by computer-generated geometric sphere models; MB-RSA, RSA method featuring analysis of head penetration by reverse engineered (scanned) cup models † bias: mean difference between the first and the second wear measurement (systematic variation of repeatability for each coordinate axis within the method) ‡ Sr, repeatability standard deviation32 § 95% repeatability limits (1.96Sr × √2): 95% limit on the difference between two test results ¶ mean of two test results (wear analyses) ** bias: the measured wear minus the accepted reference value (true wear) with a 95% CI (systematic -component of accuracy) †† RMSE, root mean square error; standard deviation of the differences between true wear and measured wear (random component of accuracy)