Last but not the least, to the extent that a more centralized government structure facilitates the cooperation of insiders in government, the level of centralization versus decentralization of the decision-making process is a valid variable.
However, considering the well known high threshold in becoming a Swiss citizen, overcome easily only by marriage, one wonders whether nationality is a valid variable to distinguish male from female offenders in this study group.
If this is not the case, then inferences may be misleading, as the association of the genetic variants with the risk factor may not be replicated in the set of individuals in which the association with the outcome is estimated, or a variant may not be a valid instrumental variable in both sets.
An outcome is said to be a valid negative control variable to the extent that it is influenced by unobserved confounders of the exposure effects on the outcome in view, although not directly influenced by the exposure.
An outcome is said to be a valid negative control variable to the extent that it is influenced by unobserved confounders of the exposure effects on the outcome in view, although not directly influenced by the exposure (3).
A genetic variable is a valid instrumental variable if the variant is associated with the risk factor of interest, the variant is not associated with any confounder of the risk factor outcome association, and the variant is conditionally independent of the outcome given the risk factor and confounders (3, 4 ).
Finally we provided an application of our method to a prediction rule with continuous predictor variables for rhabdomyolysis and showed that our method for polychotomizing continuous regressor variables can be a valid and useful tool to create probability profile tables.
To investigate whether physician's prescribing preference is a valid instrumental variable (IV) for patients' actual prescription of selective cyclooxygenase-2 (COX-2) inhibitors in the German Pharmacoepidemiological Research Database (GePaRD).
We found that distance to nearest settlement is a valid proxy variable for prediction of biomass loss from fuelwood collection (p < 0.001) and total subsistence wood extraction (p < 0.01).
No socio-economic indicator was a valid confounding variable across ethnic groups.
