Kramer et al. Respond to "Causation or 'noitasuaC'?"

Kramer et al. respond to "Composite outcomes and paradoxes".

We thank Hernán et al. (1) for their thoughtful comments about the causal relationships among exposure, birth, and perinatal death; how selection bias can distort those relationships; and the role of composite outcomes. In our article (2), we do not claim composite outcomes to be a solution (“escape”) from the selection bias caused by conditioning on birth when analyzing the effect of pregnancy...

Clayton et al. respond.

Lusk et al. respond.

We thank Schimek for his thoughtful letter. We agree that the American Association of State Highway and Transportation Officials (AASHTO) encourages bike paths; however, AASHTO’s definition of a bike path is a shared use path for pedestrians, skaters, wheelchair users, joggers, and other nonmotorized users. AASHTO discourages bicycle-only cycle tracks because, as noted by Schimek, AASHTO discou...

Nanotoxicology: Gangwal et al. Respond

Gangwal et al. (2011) addressed an important topic for nanotoxicology about assessing the toxicity of inhaled nano materials by recom mending relevant concentrations for in vitro toxicity testing. Their efforts to select in vitro concentrations based on reported occupational exposure levels of inhaled nano materials are, indeed, laudable. Their under lying conceptual approach is logical, involv...

“Phthalates”: Kelley et al. Respond