We urge caution in assuming random stratum effects for this reason.
We will use multilevel generalized linear regression models to provide statistical estimates controlling for cluster and matched stratum effects.
We assumed that within a stratum, the effect of treatment did not depend on the unobserved binary covariate.
Stratum specific effect estimates for urinary cadmium within each of four age categories (20 29, 30 39, 40 49, and 50 59 years) are presented in Table 4.
Among studies that used a two stage approach, 5/6 presented the stratum specific effect estimates, and 5/6 presented a p-value for the interaction.
We then added an interaction term between urinary cadmium and this four category age variable to obtain stratum specific effect estimates for urinary cadmium within each of these age categories.
We added a reference level-cadmium interaction term to our fully adjusted SDST models and extrapolated stratum specific effect estimates for urinary cadmium among participants with 1) less 1 μg Cd/g creatinine, 2) 1 5.24 μg Cd/g creatinine, and 3) greater than 5.24 μg Cd/g creatinine.
In these strata, the effect of low-frequency hearing level remained quite stable when adjusting for the additional variables, that is, socio-economic situation (education and position in labour market) and general health in HUNT1.
Stratum-specific effect estimates and confidence intervals were calculated directly from models that included interaction terms.
