JECH Online First, published on August 5, 2014 as 10.1136/jech-2013-203784 PostScript
LETTER
Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis In the paper entitled: “Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis publish in August 2013 issue of JECH1” some points might be of concern to your readers: 1. In the Data synthesis, authors have referred to the Relative Indexes of Inequality (RIIs) as the independent variable, while it seems that RIIs serve as measures of association (like relative risks) to show the strength of relationship between the independent variables and the outcome. 2. In the Study characteristics, it has been indicated that most of the studies were case–control (n=13). Whereas other parts of the paper (eg, in results section: “among the 23 case-control studies, 16 used hospital-based controls and the remaining 7 used population-based controls”) show that the number of case–control studies was 23. It has also been mentioned in Study characteristics that only seven studies (19%) examined the association between the incidence of gastric cancer and combined socioeconomic position (SEP), but according to table
1 and figure 5, one might conclude that there were four studies in this subgroup. 3. In the Additional analysis, figure 1 is referred to as an evidence for the absence of publication bias. This is while figure 1 is the flow diagram of search strategy and study selection process. 4. In table 1, we understand that I2 statistic is used as a measure of heterogeneity among studies; thus, is not reported when dealing with one study. But, it is not evident why I2 is mentioned for some rows (eg, the first line in ‘Education’ subgroup) but not for others (eg, the first line in other subgroups) with more than one study in the group. 5. In the Discussion, we read that in accordance with references 31–36 of the paper, genetic inheritance is among risk factors of gastric cancer which are associated with low SEP. However, this does not seem to have been an issue in any of the mentioned references. Authors of the reference 35 of the paper suggest that at least part of the excess risk of cancer among the poor relates to the aberrations in food supply and eating patterns.2 Moreover, in reference 36, hereditary diffuse gastric cancer is the focus of the paper with no previously shown association with SEP.3 Therefore, the potential association between genetics and SEP is
not implicated references.
in
any of
these
Farnaz Khatami, Mojgan Karbakhsh Department of Community Medicine, Tehran University of Medical Sciences, Tehran, Islamic Republic of Iran Correspondence to Dr Farnaz Khatami, Department of Community Medicine, Tehran University of Medical Sciences, Tehran 1412258789, Islamic Republic of Iran; [email protected] Competing interests None. Provenance and peer review Not commissioned; externally peer reviewed. To cite Khatami F, Karbakhsh M. J Epidemiol Community Health Published Online First: [ please include Day Month Year] doi:10.1136/jech-2013203784 Received 29 December 2013 Accepted 19 July 2014
▸ http://dx.doi.org/10.1136/jech-2012-201108 J Epidemiol Community Health 2014;0:1. doi:10.1136/jech-2013-203784
REFERENCES 1
2
3
Uthman OA, Jadidi E, Moradi T. Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis. J Epidemiol Community Health 2013;67:1–7. Potter JD. Diet and cancer: possible explanations for the higher risk of cancer in the poor. IARC Sci Publ 1997;138:265–83. Guilford P, Blair V, More H, et al. A short guide to hereditary diffuse gastric cancer. Hered Cancer Clin Pract 2007;5:183–94.
J Epidemiol2014. Community Health Monthby 2014 Vol 0Publishing No 0 Copyright Article author (or their employer) Produced BMJ Group Ltd under licence.
1
LETTER
Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis In the paper entitled: “Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis publish in August 2013 issue of JECH1” some points might be of concern to your readers: 1. In the Data synthesis, authors have referred to the Relative Indexes of Inequality (RIIs) as the independent variable, while it seems that RIIs serve as measures of association (like relative risks) to show the strength of relationship between the independent variables and the outcome. 2. In the Study characteristics, it has been indicated that most of the studies were case–control (n=13). Whereas other parts of the paper (eg, in results section: “among the 23 case-control studies, 16 used hospital-based controls and the remaining 7 used population-based controls”) show that the number of case–control studies was 23. It has also been mentioned in Study characteristics that only seven studies (19%) examined the association between the incidence of gastric cancer and combined socioeconomic position (SEP), but according to table
1 and figure 5, one might conclude that there were four studies in this subgroup. 3. In the Additional analysis, figure 1 is referred to as an evidence for the absence of publication bias. This is while figure 1 is the flow diagram of search strategy and study selection process. 4. In table 1, we understand that I2 statistic is used as a measure of heterogeneity among studies; thus, is not reported when dealing with one study. But, it is not evident why I2 is mentioned for some rows (eg, the first line in ‘Education’ subgroup) but not for others (eg, the first line in other subgroups) with more than one study in the group. 5. In the Discussion, we read that in accordance with references 31–36 of the paper, genetic inheritance is among risk factors of gastric cancer which are associated with low SEP. However, this does not seem to have been an issue in any of the mentioned references. Authors of the reference 35 of the paper suggest that at least part of the excess risk of cancer among the poor relates to the aberrations in food supply and eating patterns.2 Moreover, in reference 36, hereditary diffuse gastric cancer is the focus of the paper with no previously shown association with SEP.3 Therefore, the potential association between genetics and SEP is
not implicated references.
in
any of
these
Farnaz Khatami, Mojgan Karbakhsh Department of Community Medicine, Tehran University of Medical Sciences, Tehran, Islamic Republic of Iran Correspondence to Dr Farnaz Khatami, Department of Community Medicine, Tehran University of Medical Sciences, Tehran 1412258789, Islamic Republic of Iran; [email protected] Competing interests None. Provenance and peer review Not commissioned; externally peer reviewed. To cite Khatami F, Karbakhsh M. J Epidemiol Community Health Published Online First: [ please include Day Month Year] doi:10.1136/jech-2013203784 Received 29 December 2013 Accepted 19 July 2014
▸ http://dx.doi.org/10.1136/jech-2012-201108 J Epidemiol Community Health 2014;0:1. doi:10.1136/jech-2013-203784
REFERENCES 1
2
3
Uthman OA, Jadidi E, Moradi T. Socioeconomic position and incidence of gastric cancer: a systematic review and meta-analysis. J Epidemiol Community Health 2013;67:1–7. Potter JD. Diet and cancer: possible explanations for the higher risk of cancer in the poor. IARC Sci Publ 1997;138:265–83. Guilford P, Blair V, More H, et al. A short guide to hereditary diffuse gastric cancer. Hered Cancer Clin Pract 2007;5:183–94.
J Epidemiol2014. Community Health Monthby 2014 Vol 0Publishing No 0 Copyright Article author (or their employer) Produced BMJ Group Ltd under licence.
1
