"The world did not end," said Thomas Ludlam, a scientist who works on the collider.
However, there is one exception to this rule: Conditioning on a collider opens the path for statistical association through the collider along the two arrows into the collider (so there will be a statistical association between the two variables from which the arrows come, e.g., between A and B after conditioning on D in Figure 1B).
At the same time, however, conditioning on a collider may also create or contribute to an association between the colliding variables, denoted by drawing a dashed line.
Restricting the study population to ongoing pregnancies at 20 weeks thus represented stratification on a collider (survival).
In more formal language, conditioning on a collider makes marginally independent variables correlated within levels of the collider.
Furthermore, assuming that Us is an unmeasured risk factor for the previous TTP (S1) and the current TTP (S2) (Fig. 1B in Howards et al. (2012)), then S1 is a collider on a path from E to S2. Conditioning on a collider is susceptible to collider-stratification bias (Greenland, 2003; Schisterman et al., 2009).
Stratification of our analyses by smoking status could, in theory, introduce bias by conditioning on a collider (rs1051730/rs16969968).
Furthermore, because the present study was restricted to patients with CMI it is subject to the effects of conditioning on a "collider" [ 33].
Survival bias can distort associations, and such a selection bias can be viewed as a result of stratification on a collider.
Searches for this sixth and heaviest quark failed repeatedly until in April 1994 a team working on the Collider Detector Facility (CDF) at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, announced tentative evidence for the top quark.
