How to extract Bayes factor from output? (mismatch)

[jtruhs]

Maybe a simple question but here's a simple reproducible example (it happens with any example for me though):

tab <- as.table(cbind(Office=c(18,31),Phone=c(5,7)))
ctb <- contingencyTableBF(tab,sampleType = "poisson")
ctb
Bayes factor analysis
--------------
[1] Non-indep. (a=1) : 0.4968786 ±0%

Against denominator:
  Null, independence, a = 1 
---
Bayes factor type: BFcontingencyTable, poisson

ctb@bayesFactor$bf
[1] -0.6994095

I'm trying to just extract the Bayes factor of 0.4969 programmatically. When I call from the class @bayesFactor$bf it gives me a different number, and I'm not even sure it makes sense that Bayes factors can be negative?

Am I doing something wrong, and if so, what is the proper way to gather that number from the results? Thanks for your help

[bwiernik]

You're extracting the log Bayes factor. Internally it's stored that way for computational stability when the BF gets very large/small. Covert to a BF with exp().

[jtruhs]

Thank you very much. That makes so much more sense.