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Technical Question About Alphalens

Hi all,

I am not sufficiently proficient in Python to dig up the answer to this question in the source code so forgive my asking:

I have a factor, and generated a full tear sheet, with 10 quantiles (i.e. deciles). I looked "Mean Period Wise Return by Factor Quantile" barplot and saw that quantile 1 had negative mean forward returns for all three periods.

However, when I look at the dataframe generated by

 al.utils.get_clean_factor_and_forward_returns()  

and just use pandas.DataFrame.mean() on that specific quantile, the means are all positive. What's going on here?

Thank you for reading!