Academic journal article Scandinavian Journal of Work, Environment & Health

To What Degree Is the Association between Educational Inequality and Laryngeal Cancer Explained by Smoking, Alcohol Consumption, and Occupational Exposure?

Academic journal article Scandinavian Journal of Work, Environment & Health

To What Degree Is the Association between Educational Inequality and Laryngeal Cancer Explained by Smoking, Alcohol Consumption, and Occupational Exposure?

Article excerpt

In recent years, various authors aiming to assess quanti- tatively the direct and indirect effect of low educational level on laryngeal cancer risk have mentioned the rela- tionship between social inequality and laryngeal cancer. Conway and colleagues (1) calculated the percentage difference in odds ratios (OR) across sequential models including smoking, alcohol consumption, and diet and found that 67% of the excess risk for those with low education was explained by the above behaviors. This suggests that low socioeconomic status (SES) confers risk through pathways other than risky behavior. Two other studies quantitatively assessed the proportions attribut- able to lifestyle and occupational exposure adjusted for sequentially included covariates. Menvielle et al (2) explained about two-thirds of the differences observed for educational level by alcohol and tobacco consumption, varying according to tumor site. Occupational exposure explained about 50% of the remaining inequalities. Boing and colleagues (3) explained 45% of the association between low education and disease by smoking and alcohol consumption. However, they used a different definition of low education (<4 years of school).

In these studies, the extent of the association between SES and laryngeal cancer risk was measured by the difference in the regression coefficients of the same variables across models with different control variables (1-3) using the attributable fraction (AF) (ORR-ORA)/ (ORR-1), where ORR is the reference model's OR and ORA is the adjusted model's OR. However, according to Mood and others, coefficients from different nested models are not measured on the same scale in logit models and are, therefore, not directly comparable, a situation known as rescaling (4, 5). Moreover, Boing and colleagues (3) assessed the association of occupa- tion and education using models where SES variables were derived from correlated dimensions. If education and occupational class are structurally linked, inclusion of either variable would result in a similar distribution of any specific outcome (6).

The aim of our study was to estimate the contribution of behavioral and occupational risk factors to laryngeal cancer and educational aspects using a decomposition method for logit models proposed by Karlson et al (7). This approach enables assessment of the effect of con- founding without the influence of rescaling (ie, the logit coefficients are not measured on the same scale). When estimating models with nonlinear/binary outcomes, as in the logistic regression, rescaling the model after including additional covariates causes the error variance to change. Therefore, the interpretation of differences in coefficients between nested models is biased if the impact of rescaling is not taken into account (8). In our study, we used occu- pational indices that have, on the one hand, the ability to differentiate between physical-, psychosocial-, and carci- nogenic-agent-dimensions of occupation (9). On the other hand, these indices summarize occupational information for all International Standard Classification of Occupa- tions (ISCO)-coded jobs as valid job exposure matrices for many industrial sectors are not available and would not cover the range of 178 jobs (on a 3-digit ISCO-68 basis) considered in our study. The occupational dimen- sions are represented by recently developed occupational indices, which are simple to apply to occupational history data using standard ISCO coding. These indices might be able to explain a large part of the educational differences among laryngeal cancer patients.

Methods

This population-based, case-control study was con- ducted in Germany with 208 histologically confirmed male cases of laryngeal cancer (response rate 89.2%) between 1998- 2000. The study region covered a pop- ulation of 2.7 million people in the Rhein-Neckar- Odenwald region of Southwest Germany. Cases were obtained from all relevant hospitals in the region (ie, the clinics of Heidelberg, Mannheim, Ludwigshafen, Darmstadt, and Heilbronn). …

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