Correlation coefficients in ecologic studies of environment and cancer.

The objective of this study was to determine the proportion of ecologic studies published during a 20-year period regarding environmental exposures and cancer in which correlation coefficients or coefficients of determination were used as a measure of association. The authors performed a descriptive analysis of published literature by conducting a systematic review of PubMed to identify eligible ecologic studies published between 1991 and 2010. The reported measure of association was extracted for all eligible studies. During the 20-year study period, 35/105 (33%, 95% confidence limits [CL]: 25%, 43%) ecologic studies used correlation coefficients or coefficients of determination as a measure of association. These results indicate that the use of correlation coefficients and coefficients of determination as measures of association in ecologic studies of environmental exposures and cancer is relatively common, despite extensive literature discouraging their interpretation as valid measures of association.

The association between renal cell carcinoma and multiple myeloma: insights from population-based data.

OBJECTIVE: • To evaluate the hypothesis of an association between renal cell carcinoma and multiple myeloma. PATIENTS AND METHODS: • Data from nine population-based registries in the Surveillance, Epidemiology and End Results programme were used to evaluate two separate cohorts of patients diagnosed between 1973 and 2006: patients diagnosed with renal cell carcinoma as a primary malignancy (n= 57,190) and patients diagnosed with multiple myeloma as a primary malignancy (n= 34,156). • We estimated standardized incidence ratios (SIRs) with corresponding 95% confidence intervals (CIs) by dividing the number of observed cases of multiple myeloma within the renal cell carcinoma cohort and the number of renal cell carcinoma cases within the multiple myeloma cohort by the number of expected cases for each malignancy in the US general population. RESULTS: • The renal cell carcinoma cohort yielded 88 multiple myeloma cases during 293,511 person-years of follow up. Patients with renal cell carcinoma had a higher relative risk of multiple myeloma than the general population (SIR = 1.51, 95% CI 1.21-1.85). • The multiple myeloma cohort yielded 69 renal cell carcinoma cases during 100,804 person-years of follow up. Patients with multiple myeloma had a higher relative risk of renal cell carcinoma than the general population (SIR = 1.89, 95% CI 1.47-2.40). CONCLUSION: • Our analyses revealed a bidirectional association between renal cell carcinoma and multiple myeloma, which typically indicates shared risk factors.