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Good peer reviewing?
- Stefano Belli (25 June 2007)
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Stefano Belli, senior epidemiologist Ist. Sup. di Sanità - Rome, Italy
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To: Johan P. Mackenbach Editor-in-chief Walter Ricciardi Editor Giuseppe Costa Associate editor Rodolfo Saracci Dear Editors, I just read the paper “All causes mortality in male professional soccer players” by Emanuela Taioli published by The European Journal of Public Health (April 12, 2007, 1-5). The paper is characterized by a number of informal procedures and questionable assessments. 1. Section “Materials and methods”, paragraph “Ascertainment of vital status” No reference is given concerning the computational facility used. No mention is made about the level of disaggregation of person-years by age class (5 year age classes? 10 year age classes?) and calendar period (5 year calendar periods? which periods?) 2. Section “Materials and methods”, paragraph “Search for causes of death” It is apparent that several distinct sources of information were used to achieve causes of death. Most of them are quite unusual for classic epidemiologists, being the final contrast versus rates based only on official documents (death certificates). 3. Section “Materials and methods”, paragraph Statistical analysis - Mortality rates The author says: “… subject-years of follow-up were calculated from the date at the first appearance in an Italian or foreign Championship (as indicated by Panini Company) until 31 December 2003, or the date of death or the date of the last follow-up, for a total of 101 878 subject-years of follow-up.”. In cohort studies a starting point for the follow-up is necessary to define a time window of observation. This date must be the same for all the subjects in the study. Previous dates can be useful for computing latency periods, but they must not be considered while computing person- years. In this case a bias is introduced: all the person-years relative to the period anterior to the start date are dependent on the vital status of the subjects in the study. There is a contribution to the denominator without any possibility to contribute to the numerator (selection bias). 4. Section “Materials and methods”, paragraph Statistical analysis - Methods for deriving the expected number of deaths and for calculation of Standardized Mortality Ratios (SMRs). The author says: “Expected rates were calculated for men aged 15–69 years, in order to represent the age range observed in the cohort of soccer players.”. The concept itself of “expected rates” in cohort studies is unknown to classic epidemiology. 5. In the same section, following lines, the author illustrates the various sources used to get some kind of reference mortlity rates. The author justifies her choice in the discussion with the affirmation “given the lack of age-and gender-specific mortality rates for Italy”. This is completely false. A number of cohort studies conducted in Italy by eminent epidemiologists are published yearly by outstanding journals. ISTAT (the National Institute in charge of producing vital statistics) publishes yearly updates of Italian mortality rates by age class and gender. This information is made available for all the scientists working in the field of epidemiology. 6. Section “Results” The author says: “A survival analysis was performed on this cohort, to assess the independent effect of Body Mass Index, length of professional career in years, overall number of official games played, position played within the team, and calendar year of starting of professional activity. For overall mortality the length of professional career was protective against death, although not significantly.” This assessment sounds rather funny. On a conceptual ground, the length of professional carreer is a consequence, not a determinant, of a favourable vital status. The reading of some old paper from the eighties dealing with the difference between statistical significance and causal association might be still useful with this respect. In conclusion, this paper neither gives further information on the topic nor appears as an innovative approach in classic epidemiology. Morever, this qualitatively poor contribution places our Country and all the scientists working in the field of epidemiolgy in a unfavourable light, denying the availability of any vital statistics in Italy. I wonder how such an astonishing paper could ever be published at all. Best regards dr. Stefano Belli Senior Epidemiologist Ist. Sup. di Sanità Rome (Italy) Conflict of Interest:None declared |
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