Outcomes method for biomarkers

[nhejazi]

It appears that the idea of considering the impact of biomarkers on some kind of outcome measures was rather ill-conceived -- that is, with the current use of tmle::tmle for assessing the impact of biomarkers (on some kind of outcome via the ATE) requires that the expression measures associated with the biomarkers be discretized.

Generally speaking, there does not exist a reasonable way to discretize expression measures -- there is great disagreement in the genomics / high-dimensional biology literature -- and any estimates based on discretized biomarker expression values are likely to be un-meaningful scientifically.

[nhejazi]

For now, it's best to remove the outcome option in the main biomarkertmle function. In future, we can consider ways to approach this -- with the most obvious idea being to estimate a different parameter entirely (than the ATE), perhaps using the tmle.npvi package.

[nhejazi]

It seems that the implementation of a TMLE for a target parameter interpretable as the counterfactual value of the outcome of interest under a posited shift of the observed treatment value, available in the txshift R package, could be useful for this purpose.

[nhejazi]

At the present, implementing such an extension of the methodology appears to be outside the scope of this R package.

[nhejazi]

Outside the scope of this package. An equivalent shrinkage-based variance estimator should likely be implemented separately in other packages so as to better make use of each of their (likely very different) APIs.