Wordfish results change from run to run

[chriswratil]

Hi,

the textmodel_wordfish() function does not give the exact same results in two runs in case the DFM is sparse. Is this due to the use of an approximation to the SVD if the DFM is sparse? In any case, it would be great to add a possibility of deterministic results in case the DFM is sparse. This would be important for replication purposes.

To see the problem, just run the following a few times and compare the last digits of the theta estimates.

library(quanteda)
summary(textmodel_wordfish(dfm(data_corpus_inaugural)))

Thanks so much for your support and best wishes,

Chris

[koheiw]

Thank you for the post. It is related to random initial values for sparse implimentation:

quanteda/src/wordfish_mt.cpp

Line 331 in 76e2cbf

std::mt19937 mt(time(0)); // issue #1063

We will try to fix.

[kbenoit]

I've changed the default to sparse = FALSE. Doesn't solve the fundamental issue, but will stop the difference in results from repeating the function call.