We thank Drs. Sabour and Ghassemi for their interest in our paper and for their didactic attention to the correct analytic methods for quantifying the test-retest reliability of a measurement method, the intraclass correlation coefficient (ICC),1 and agreement between measurements made with two different methods, the Bland-Altman analysis.2 We did, in fact, use the single measure ICC. Both of these statistical techniques, not just the former, played an important role in our analysis which led to our conclusion, which we stand by. The SightBook mobile app has excellent test-retest reliability and so can be usefully employed to follow acuity over time, as long as baseline measurements are made with the SightBook. However, there are clinically substantial differences, quantified with the Bland-Altman Limits of Agreement, between SightBook measurements and those made using near cards or Snellen charts. This means that SightBook acuity measurements should not be used at follow-up to compare against baseline measurements made with one of the other methods.
Acknowledgments
Supported by NIH Center Core Grant P30EY014801, Research to Prevent Blindness
Unrestricted Grant, Department of Defense (DOD-Grant#W81XWH- 09-1- 0675).
The sponsor or funding organization had no role in the design or conduct of this research.
Footnotes
None of the authors have any conflicts of interest to disclose.
References
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