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RESEARCH: Ane Cecilie Dale, Lars J Vatten, Tom Ivar Nilsen, Kristian Midthjell, and Rune Wiseth Secular decline in mortality from coronary heart disease in adults with diabetes mellitus: cohort study BMJ 2008; 337: a236 [Abstract] [Full text]

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There seems to be apparent computation errors in the paper. They should be clarified or corrected.

Arya K Kumarasena   (16 July 2008)

The authors reply to the rapid response: "There seems to be apparent computation errors in the paper. They should be clarified or corrected."

Ane Cecilie Dale, Lars J Vatten, Tom Ivar Nilsen, Kristian Midthjell, Rune Wiseth   (13 August 2008)

There seems to be apparent computation errors in the paper. They should be clarified or corrected. 16 July 2008
Arya K Kumarasena, Consultant/Director Metropolitan Group, 85,Braybrooke Place,Colombo2,Sri Lanka Send response to journal: Re: There seems to be apparent computation errors in the paper. They should be clarified or corrected.	The paper provides the person years of males and females with and without diabetes for both surveys HUNT1 and HUNT2 [1]. Highest number of deaths and morality rates are associated with 80 + person groups. Research publications [2] and [3] provides further details on HUNT surveys .According to them there were 2143 females in 80+ group in HUNT2 database(1906:80-89group, 237:90+group). Out of them 263 persons were diabetic patients (12.83%:80-89 group, 12.24%:90+group).Therefore there should be 1980 others. As the HUNT2 survey started in August 1995 and person year computation was based on the 31st December 2004 survivors, person years contribution from each and every person will be less than 9.5 years. (Late recruits and deceased will have much shorter periods). Therefore total number of person years of this category cannot exceed 18810 years (1980*9.5). How ever the figure indicated in the paper is 21480 years, which shows an apparent computation error? Similar scenario exists for all groups of 80+ non diabetic persons. As the increase in person years will directly reduce the morality rate, apparent error will effect the final conclusion. Therefore clarification or correction seems to be necessary. Indication of Mortality rate (95%CI) derived from only one death and application of statistical techniques to correlate mortality rates of two groups having around 18 years difference in mean age values may also provide results with very little meaning. [1] Published 1 July 2008, doi:10.1136/bmj.39582.447998.BE BMJ 2008;337:a236 Research Secular decline in mortality from coronary heart disease in adults with diabetes mellitus: cohort study Ane Cecilie Dale, research fellow, medical doctor, Lars J Vatten, professor, Tom Ivar Nilsen, associate professor, Kristian Midthjell, associate professor, Rune Wiseth, professor [2] K Midthjell, O Kruger, J Holmen, A Tverdal, T Claudi, A Bjorndal, and P Magnus Rapid changes in the prevalence of obesity and known diabetes in an adult Norwegian population. The Nord-Trondelag Health Surveys: 1984-1986 and 1995-1997 Diabetes Care 22: 1813-1820. [3] Holmen J, Midthjell K, Krüger Ø, Langhammer A, Holmen TL, Bratberg GH, et al. The Nord-Trøndelag health study 1995-97 (HUNT 2): objectives, contents, methods and participation. Nor J Epidemiol 2003;13:19-32. Competing interests: None declared
The authors reply to the rapid response: "There seems to be apparent computation errors in the paper. They should be clarified or corrected." 13 August 2008
Ane Cecilie Dale, research fellow, medical doctor StOlavs Hospital, Trondheim, Norway, Lars J Vatten, Tom Ivar Nilsen, Kristian Midthjell, Rune Wiseth Send response to journal: Re: The authors reply to the rapid response: "There seems to be apparent computation errors in the paper. They should be clarified or corrected."	Based on the number of participants reported in other publications from the HUNT Study, Kumarasena (1) has calculated the number of person years that may be obtained during 9.5 years of follow up, as in our recent paper in BMJ (2). She claims that the person years that we report for the age group 80 years and older must be incorrect (i.e. the number given in the paper is 21480 person years for women without diabetes, and Kumarasena suggests that this number should not exceed 18810 person years). In the analysis mortality rates were calculated using the stsplit command in Stata. This procedure expands the individual survival record into information on time at risk for an event to occur for different categories of time (in the present study, that means age categories; younger than 60 years, 60-69, 70-79, and 80 years and older). As a consequence, the number of person years for individuals in a certain age group at baseline cannot be simply calculated as the sum of the observation time for people within that category. For example, consider a woman who was 77 years at baseline, and seven years later, at the age of 84, died from coronary heart disease. In the analysis, this woman will contribute three years of person time to the denominator for the age-group 70-79 years, and four years for the age group 80 years and older. The event (i.e. her death from coronary heart disease) will be counted in the numerator of the age group 80 years and older, and not in the age group 70 -79 years, although she belonged to the latter category at baseline. This approach is widely regarded as an appropriate way to handle time at risk data, especially for long follow-up periods, and we hope this clarification is satisfactory. Ane Cecilie Dale, Lars J Vatten, Tom Ivar Nilsen, Kristian Midthjell, Rune Wiseth (1) Arya K Kumarasena. There seems to be apparent computation errors in the paper. They should be clarified or corrected. Published 16 July 2008, BMJ. (2) Dale AC, Vatten LJ, Nilsen TI, Midthjell K, Wiseth R. Secular decline in mortality from coronary heart disease in adults with diabetes mellitus: cohort study. BMJ 2008 Jul 1;337:a236. doi: 10.1136/bmj.39582.447998. BE. Competing interests: None declared