Does quality of observational studies affect the results of a meta-analysis?: the case of cigarette smoking and pancreatic cancer.
OBJECTIVE
A meta-analysis of observational studies on association between cigarette smoking and pancreatic cancer was performed to focus, particularly, on the role of the studies' quality in affecting meta-analysis results.


METHODS
A bibliographic search was carried out on PubMed and EMBASE databases until February 15, 2008. Key words were "pancreatic neoplasms," "pancreatic cancer," "smoking," "smoke," "cigarette," "case-control studies," and "cohort studies." Studies about cigarette smoking and pancreatic cancer were selected and assessed on quality. STATA 9.0 was used.


RESULTS
Six cohort studies and 24 case-control studies were selected, with median quality scores of 8 (range, 3) and 10 (range, 8), respectively. Pooled case-control studies' odds ratio (OR) and cohort studies' risk ratio were, respectively, 1.45 (95% confidence interval [CI], 1.33-1.57) and 1.78 (95% CI, 1.64-1.92). After stratifying for quality scoring, high-quality-scored case-control studies yielded an OR of 1.38 (95% CI, 1.27-1.49), whereas the others gave an OR of 1.52 (95% CI, 1.34-1.73). The results of meta-analysis for cohort studies showed a risk ratio of 1.74 (95% CI, 1.61-1.90) and of 2.10 (95% CI, 1.64-2.67), respectively, for high- and low-quality score studies.


CONCLUSIONS
There is evidence that cigarette smoking is an important risk factor for pancreatic cancer, but the estimate of the association greatly relies on the studies' quality.
La Torre
Giuseppe
G
Epidemiology and Biostatistics Unit, Institute of Hygiene, Catholic University of the Sacred Heart, Rome, Italy. giuseppe.latorre@rm.unicatt.it
de Waure
Chiara
C
Specchia
Maria Lucia
ML
Nicolotti
Nicola
N
Capizzi
Silvio
S
Bilotta
Antonella
A
Clemente
Gennaro
G
Ricciardi
Walter
W
D016022:Case-Control Studies; D015331:Cohort Studies; D006801:Humans; D010190:Pancreatic Neoplasms / Q000453:epidemiology*; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*