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David Fox

RESOLUTION

See companion Issue#38.

Also, note Aldenberg (2015) does not discuss censored data.

David Fox

RESOLUTION

·        Response to reviewer:

We are a little perplexed by the statement “There is hardly a mention of censoring”. The section “Left-tail weighting of the SSD” is devoted to the use of censoring as a means of increasing the weight in the left tail of the SSD. However, we appreciate that this is perhaps not the type of censoring the reviewer had in mind. The other kind of censoring is the <DL type that is a consequence of the measurement process. This type of data is frequently encountered in ecotox. and it is well accommodated for in existing software packages including MOSAIC, ssdtools, and SSD Toolbox. Consistent with the stated aims and scope of the MS, we do not feel any additional discussion is warranted.

Joe Thorley

I would just like to point out that ssdtools handles censored data correctly (if the distributions have the same number of parameters because the sample size is irrelevant for comparing model weights) – it’s on the to do list to enforce this condition in ssdtools.

Carl Schwarz

Also see Wheeler and Bailer paper that I also put in another comment.

David Fox

Wheeler and Bailer (2009) don’t mention censoring.

Carl Schwarz

See the paper by Nysen et al (2016) that I refer to in a separate comment who show how this can be done and is used.

If we want to include censored endpoints, we could do it via maximum likelihood but it might be easier to use Bayesian methods. See Angelina and my manscript on using Bayesian methods.

Aldenberg (2015) does not discuss censored data.

David Fox

We agree that censoring is an important topic, however it is not a focal point of the MS. Our mention and use of censoring has been in the context of the stated and discussed problem of left-tail weighting not censoring per se. One of the strategies for increasing the weight of observations in the left-tail of the SSD is to censor some fraction of observations in the right tail of the SSD. It was never our intent to have a fuller discourse on the treatment of censored data. While the concepts are related, there’s a subtle distinction between how to incorporate and use censored toxicity data in SSD fitting and the process of deliberately censoring some data for left-tail weighting.

My view is we maybe add some text in the MS to this effect.

Finally – I disagree with the assertion there is not yet a general agreement on how, or even whether, such data should be analyzed for SSD purposes”. As we point out, MOSAIC and SSD Tollbox do handle censoreed data and they do that in a statistically legitimate way.