La prolongada presencia del invierno

In conclusion, we found that agreement for self-reported sun exposure was moderate and could lead to a substantial attenuation of the observed odds ratio in a case-control study. Agreement of an objective measure of cumulative lifetime sun exposure, actinic damage, was substantial. There was no evidence that the reliability for different exposure measures was lower in cases compared to controls, and reassuringly, among cases, there were no differences in reliability by subgroups of disease related factors such as disability (EDSS score), disease duration or type of MS. This provides confidence that even if there was some degree of cognitive dysfunction among cases, it is not likely to affect the results of the MS case-control study. No differences were observed in the agreement of self-reported sun exposure by sex, education, melanin density at the upper inner arm, ability to recall sun exposure or interviewer, but the agreement differed slightly by age.

6.6 S

Measurement error of exposure variables is one of the major sources of bias in case-control studies. It was our objective in this chapter to assess the reliability of measures of past sun exposure and to examine whether self-reported sun exposure differed by disease status or other variables, such as age, gender, education, melanin density at the upper inner arm, and ability to recall sun exposure. A measure-retest comparison was conducted on 52 prevalent cases and 52 community controls, who were re-interviewed after 11 weeks on average. In addition, questionnaire administration of 136 cases and 272 controls of a validated sun exposure question for different age periods was compared to the use of this question in a life events calendar, where memorable events were used as guideposts. We found that

agreement for self-reported sun exposure was moderate and similar for the two comparison methods. Agreement of an objective measure of cumulative lifetime sun exposure–actinic damage–was substantial. There was no evidence that the reliability for different exposure measures was lower in cases compared to controls, and reassuringly, among cases there were no differences in reliability by subgroups of disease related factors such as disability (EDSS score), disease duration or type of MS. Also, no differences were observed in the

agreement of self-reported sun exposure by sex, education, melanin density at the upper inner arm, ability to recall sun exposure or interviewer, but the agreement differed slightly by age. In conclusion, the moderate agreement for self-reported sun exposure found in this study could lead to a substantial attenuation of the observed odds ratio in a case-control study, while the similar reliability between cases and controls suggests that, even if there was some degree of cognitive dysfunction among cases, it is unlikely to affect the results of the Tasmanian MS case-control study.

6.7 P

In this chapter we discussed the reliability of one of our main exposures of interest–sun exposure. We found that self-reported sun exposure is recalled only with moderate agreement, which could lead to a substantial attenuation of the observed odds ratio in our Tasmanian MS case-control study, and could limit us in finding an association. The reliability of actinic damage, an objective measure of cumulative lifetime sun exposure, was however, substantial. The results of the case-control study in regard to the UVR hypothesis (whether high levels of past UVR exposure is related to a decreased risk of MS) will be discussed in chapter 8. The next chapter will focus on the reliability of the spectrophotometric assessment of skin type.

6.8 R

1. Armstrong BK, White E, Saracci R. Principles of exposure measurement in epidemiology. Oxford: Oxford University Press, 1992.

2. Means B, Swan GE, Jobe JB, Esposito JL. An alternative approach to obtaining personal history data. In: Biemer PP, Groves RM, Lyberg LE, Mathiowetz NA, Sudman S, eds. Measurement Errors in Surveys. New York: John Wiley & Sons, 1991:167-183.

3. Hoppin JA, Tolbert PE, Flagg EW, Blair A, Zahm SH. Use of a life events calendar approach to elicit occupational history from farmers. Am J Ind Med 1998; 34:470-6. 4. Friedenreich CM, Courneya KS, Bryant HE. The lifetime total physical activity

questionnaire: development and reliability. Med Sci Sports Exerc 1998; 30:266-74. 5. Krall EA, Valadian I, Dwyer JT, Gardner J. Accuracy of recalled smoking data. Am J

Public Health 1989; 79:200-2.

6. Kricker A, Armstrong BK, English DR, Heenan PJ. Does intermittent sun exposure cause basal cell carcinoma? a case-control study in Western Australia. Int J Cancer 1995; 60:489-94.

7. Kricker A, Armstrong BK, English DR, Heenan PJ. A dose-response curve for sun exposure and basal cell carcinoma. Int J Cancer 1995; 60:482-8.

8. Rao SM, Leo GJ, Bernardin L, Unverzagt F. Cognitive dysfunction in multiple sclerosis. I. Frequency, patterns, and prediction. Neurology 1991; 41:685-91. 9. Rao SM. Neuropsychology of multiple sclerosis. Curr Opin Neurol 1995; 8:216-20. 10. Amato MP, Ponziani G, Siracusa G, Sorbi S. Cognitive dysfunction in early-onset

multiple sclerosis: a reappraisal after 10 years. Arch Neurol 2001; 58:1602-6. 11. Dwyer T, Blizzard L, Gies PH, Ashbolt R, Roy C. Assessment of habitual sun

exposure in adolescents via questionnaire-a comparison with objective measurement using polysulphone badges. Melanoma Res 1996; 6:231-9.

12. Jones G, Blizzard C, Riley MD, Parameswaran V, Greenaway TM, Dwyer T. Vitamin D levels in prepubertal children in Southern Tasmania: prevalence and determinants. Eur J Clin Nutr 1999; 53:824-9.

13. Thieden E, Agren MS, Wulf HC. Solar UVR exposures of indoor workers in a Working and a Holiday Period assessed by personal dosimeters and sun exposure diaries. Photodermatol Photoimmunol Photomed 2001; 17:249-55.

14. Holman CD, Evans PR, Lumsden GJ, Armstrong BK. The determinants of actinic skin damage: problems of confounding among environmental and constitutional variables. Am J Epidemiol 1984; 120:414-22.

15. Green AC. Premature ageing of the skin in a Queensland population. Med J Aust 1991; 155:473-4, 477-8.

16. Beagley J, Bibson IM. Changes in skin condition in relation to degree of exposure to ultraviolet light. Perth: Western Australia Institute of Technology, School of Biology, 1980.

17. Cohen JA. A Coefficient of agreement for nominal scales. educational and psychological measurement 1960; XX:37-46.

18. Cohen JA. nominal scale agreement with provision for scaled disagreement or partial credit. American Psychological Association 1968; 70:213-219.

19. Cicchetti DV, Allison T. A new procedure for assessing reliability of scoring eeg sleep recordings. American Journal of Eeg Technology 1971; 11:101-109.

20. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977; 33:159-74.

21. Shrout PE, Fleiss JL. Intraclass correlations: Uses in assessing rater reliability. Psychol Bull 1979; 86:420-428.

22. Armitage P, Berry G. Statistical methods in medical research. London: Blackwell Scientific Publications, 1987:93-140.

23. English DR, Armstrong BK, Kricker A. Reproducibility of reported measurements of sun exposure in a case-control study. Cancer Epidemiol Biomarkers Prev 1998; 7:857-63.

24. Rosso S, Minarro R, Schraub S, Tumino R, Franceschi S, Zanetti R. Reproducibility of skin characteristic measurements and reported sun exposure history. Int J Epidemiol 2002; 31:439-46.

25. Blizzard L, Dwyer T, Ashbolt R. Changes in self-reported skin type associated with experience of sunburning in 14-15 year old children of northern European descent. Melanoma Res 1997; 7:339-46.

26. Branstrom R, Kristjansson S, Ullen H, Brandberg Y. Stability of questionnaire items measuring behaviours, attitudes and stages of change related to sun exposure. Melanoma Res 2002; 12:513-9.

27. Berwick M, Chen YT. Reliability of reported sunburn history in a case-control study of cutaneous malignant melanoma. Am J Epidemiol 1995; 141:1033-7.

28. Westerdahl J, Anderson H, Olsson H, Ingvar C. Reproducibility of a self-administered questionnaire for assessment of melanoma risk. Int J Epidemiol 1996; 25:245-51. 29. Fleiss JL, Cohen JA. The equivalence of weighted kappa and the intravlass

correlation coefficient as measures of reliability. Educational and psychological measurement 1973; 33:613-619.

30. Nunnally JC. Psychometric Theory. London: McGraw-Hill, 1978.

31. Whiteman D, Green A. Wherein lies the truth? Assessment of agreement between parent proxy and child respondents. Int J Epidemiol 1997; 26:855-9.

32. Fortes C. Reproducibility of skin characteristic measurements and reported sun exposure history. Int J Epidemiol 2002; 31:446-8.

33. Paffenbarger RS, Jr., Lee IM, Kampert JB. Physical activity in the prevention of non- insulin-dependent diabetes mellitus. World Rev Nutr Diet 1997; 82:210-8.

34. Friedenreich CM. Improving long-term recall in epidemiologic studies. Epidemiology 1994; 5:1-4.