Survivor bias – and its impact on studies of treatments in pregnancy

How can a lower still birth rate in pregnant women who have taken some treatment (such as a vaccine) during pregnancy mean that they are at higher risk of a still birth? It is all about what stage of their pregnancy they get the treatment – there is ‘survivor bias’ in those treated late in pregnancy.

I present an analogy of a marathon race based on one suggested by colleague Prof Retsef Levi.
Full details: https://www.normanfenton.com/post/the-statistical-illusion-of-better-pregnancy-outcomes-for-vaccinated-women