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OPERATIONAL EVALUATION OF THE USE OF PHOTOGRAPHS FOR GRADING ACTIVE TRACHOMA

We evaluated the reliability of photographs to verify field diagnoses of active trachoma. We examined 956 residents of a trachoma-endemic village for signs of trachoma using the World Health Organization simplified grading system. Two photographs of the right eye of 948 persons were independently graded (masked to field assessment) by the field examiner and two other experienced graders. There was only moderate agreement between field assessment and the subsequent photographic evaluations by the three graders. When we counted ungradable photographs as disagreements, mean kappa scores for the signs trachomatous inflammation (follicular [TF]) and trachomatous inflammation (intense [TI]) were 0.44 and 0.51, respectively. There was also only fair-to-moderate agreement between the three assessments (by different examiners) of the photographs. Either the signs TF and TI themselves are not as reliable as previously believed, or photographs should be used for their diagnosis only when reliability testing demonstrates better agreement than found here.

Received May 18, 2005. Accepted for publication September 28, 2005.

Acknowledgments: We thank the village and sub-village chairmen, elders, and villagers of Kahe for their enthusiastic participation; our field team for help with data collection; Dr. Paul Emerson for helpful conversations about the use of photographs; and Professor John Shao and the members of the research steering committee.

Financial support: This study was supported by grants from the Wellcome Trust/Burroughs Wellcome Fund (059134) and the Edna McConnell Clark Foundation (99100).

^* Address correspondence to Anthony W. Solomon, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom. E-mail: anthony.solomon{at}lshtm.ac.uk

Authors’ addresses: Anthony W. Solomon, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom, Telephone: 44-20-7958-8336, Fax: 44-20-7958-8317, E-mail: anthony.solomon{at}lshtm.ac.uk. Richard J. C. Bowman, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom, Telephone: 44-20-7958-8359, Fax: 44-20-7958-8317, E-mail: richardbowman{at}intafrica.com. David C. W. Mabey, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom, Telephone: 44-20-7927-2297, Fax: 44-20-7637-4314, E-mail: david.mabey{at}lshtm.ac.uk. David Yorston, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, United Kingdom, Telephone: 44-20-7253-3411, Fax: 44-20-7253-4696, E-mail: dhyorston{at}enterprise.net. Patrick A. Massae, Rombo Trachoma Research Project, Huruma Hospital, PO Box 202, Mkuu, Rombo, Tanzania, Telephone: 255-27-275-7230, E-mail: patrick.massae{at}iwayafrica.com. Salesia Safari, Huruma Hospital, PO Box 948 Moshi, Tanzania, Telephone: 255-27-275-7136, Fax: 255-27-275-7341, E-mail: huruma.hospital{at}iwayafrica.com. Brian Savage, 91 Drewry Lane, Derby DE22 3QS, United Kingdom, Telephone: 44-1332-242-635, E-mail: Able4{at}btinternet.com. Neal D. E. Alexander, Infectious Diseases Epidemiology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom, Telephone: 44-20-7927-2483, Fax: 44-20-7636-8739, Email: neal.alexander{at}lshtm.ac.uk. Allen Foster, International Centre for Eye Health, Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom, Telephone: 44-20-7958-8359, Fax: 44-20-7958-8317, E-mail: allenfoster{at}compuserve.com.

The kappa statistic is an index of intra-observer or inter-observer reliability for categoric data. It is the difference between the observed and chance values of the proportion of agreement between two sets of observations of the same variable, expressed as a proportion of this difference’s maximum value.⁷ Kappa therefore has possible values between –1 and +1, with –1 indicating complete disagreement, +1 complete agreement, and 0 the level of agreement expected by chance. Divisions for describing the relative strength of agreement associated with this measurement have been (arbitrarily) defined as poor = 0.00; slight = 0.00–0.20; fair = 0.21–0.40; moderate = 0.41–0.60; substantial = 0.61–0.80; and almost perfect = 0.81–1.00.⁸