Recovering true risks when multilevel exposure and covariables are both misclassified

The effects of joint misclassification of exposure and disease on the attributable risk

While there is extensive methodological literature analysing the effects of misclassification on the relative risk under various misclassification scenarios, for the attributable risk only the effects of non-differential misclassification either of exposure or disease, and the effects of non-differential independent misclassification of exposure and disease have been discussed for the 2 x 2-situation. The paper investigates the effects of non-differential correlated misclassification of exposure and disease on the attributable risk taking possible correlations of both types of misclassification into account. Furthermore, a comparison with the corresponding effects on the relative risk is drawn. We propose a matrix-based approach to describe the underlying structure of non-differential misclassification. The bias arising from non-differential misclassification in the attributable risk and relative risk is evaluated in four examples assuming under- or overreporting of exposure and disease. In each of the four examples we found scenarios where pronounced differences in degree and, more importantly, in direction of bias occurred. Our results clearly demonstrate the danger lying in the stereotype transfer of findings regarding misclassification effects on the relative risk to other epidemiologic risk measures and underline the necessity of specific analyses of the effects of misclassification on the attributable risk.

Interaction between topography and coating in the formation of bone nodules in culture for hydroxyapatite- and titanium-coated micromachined surfaces

Rat osteoblast cultures were maintained from 24 h to 6 weeks on hydroxyapatite (HA)- or titanium (Ti)-coated smooth and micromachined grooved substrata in medium supplemented with L-ascorbic acid-2-phosphate and beta-glycerophosphate to promote mineralization. The HA coatings, approximately 1 microm thick, were characterized using X-ray diffraction, surface roughness, and scanning electron microscopy (SEM). Osteoblasts elongated, aligned, and moved in the direction of the grooves on both Ti and HA grooved surfaces. HA surfaces produced significantly more bone-like nodules than Ti surfaces. All grooved substrata produced significantly more nodules than smooth surfaces. These results are consistent with the hypothesis that substrata can increase osteogenesis by formation of an appropriate microenvironment. There was also a statistically significant interaction between topography and chemistry in the formation of mineralized nodules. A strong correlation (r = 0.958) between alkaline phosphatase (Alk-P) at 2 weeks and nodule counts at 6 weeks was observed, suggesting that Alk-P may possibly be used as a leading indicator of osteogenesis on microfabricated surfaces. The results of this study indicate that surface topography and chemistry can affect osteogenesis, and that interactions between chemistry and topography can occur.