July 2012
Volume 53, Issue 8
Free
Letters to the Editor  |   July 2012
Accuracy, Validity, and Reliability of the Infrared Optical Head Tracker (IOHT)
Author Affiliations & Notes
  • Siamak Sabour
    The Department of Clinical Epidemiology, Shahid Beheshti University of Medical Sciences, Tehran, Iran; and
  • Fariba Ghassemi
    Eye Research Centre, Farabi Hospital, Tehran University of Medical Sciences, Tehran, Iran.
Investigative Ophthalmology & Visual Science July 2012, Vol.53, 4776. doi:10.1167/iovs.12-10324
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    • Get Citation

      Siamak Sabour, Fariba Ghassemi; Accuracy, Validity, and Reliability of the Infrared Optical Head Tracker (IOHT). Invest. Ophthalmol. Vis. Sci. 2012;53(8):4776. doi: 10.1167/iovs.12-10324.

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      © ARVO (1962-2015); The Authors (2016-present)

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Introduction
Wewere interested to read the paper by Kim et al., published in the March 2012 issue of Investigative Ophthalmology & Visual Science. 1 The authors aimed to evaluate the accuracy, validity, and reliability of a newly developed infrared optical head tracker (IOHT) using Nintendo Wii remote controllers (WiiMote; Nintendo Co. Ltd., Kyoto, Japan) for measurement of the angle of head posture. They reported that, in comparison with the data from the cervical range of motion (CROM), the IOHT-derived results showed high consistency. 1 Why did the authors not use seven well known statistical tests to evaluate validity of IOHT compared to CROM as gold standard (sensitivity, specificity, positive predictive value [PPV], negative predictive value [NPV], likelihood ratio positive and negative [LR+ and LR−], and odds ratio)? 25 Moreover, high consistency between IOHT and CROM results neither prove reliability nor validity of IOHT. 25 They reported that correlation coefficients of 1- and 3-D positions between the IOHT and the CROM were more than 0.99 and 0.96 (P < 0.05, Pearson's correlation test), respectively. 1 Pearson's correlation has nothing to do with reliability as well as validity, and actually is one of the common mistakes in reliability analysis. 25 As the authors point out in their conclusion, the IOHT showed strong concordance with the CROM, thus proving its validity and reliability as a head-posture-measuring device. 1 Why did they not use intra-class correlation coefficient (ICC) exact type or weighted kappa to evaluate the reliability of IOHT? 25 It is good to know that validity (accuracy) and reliability (precision) are two completely different issues being evaluated with different tests that should be interpreted with caution.2–5  
References
Kim J Nam KW Jang IG Yang HK Kim KG Hwang JM. Nintendo Wii remote controllers for head posture measurement: accuracy, validity, and reliability of the infrared optical head tracker. Invest Ophthalmol Vis Sci . 2012; 53:1388–1396. [CrossRef] [PubMed]
Jeckel JF Katz DL Elmore JG Wild DMG. Epidemiology, Biostatistics and Preventive Medicine. 3rd ed. Philadelphia, PA: W.B. Saunders Co.; 2007.
Rothman KJ Greenland S Lash TL. Modern Epidemiology. 4th ed. Baltimore, MD: Williams & Wilkins; 2010.
Szklo M Nieto FJ. Epidemiology Beyond the Basics. 2nd ed. New York, NY: Jones and Learning; Bartlett 2007.
Bland JM Altman DG. Agreed statistics: measurement method comparison. Anesthesiology . 2012; 116:182–185. [CrossRef] [PubMed]
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