title: freq argument options in statsmodels tsa AR and ARMA models
body: <p>In the statsmodels time series analysis <a href="http://statsmodels.sourceforge.net/devel/generated/statsmodels.tsa.ar_model.AR.html#statsmodels.tsa.ar_model.AR" rel="nofollow">AR</a> and <a href="http://statsmodels.sourceforge.net/devel/generated/statsmodels.tsa.arima_model.ARMA.html#statsmodels.tsa.arima_model.ARMA" rel="nofollow">ARMA</a> models, the <code>freq</code> argument can be "a Pandas offset or ‘B’, ‘D’, ‘W’, ‘M’, ‘A’, or ‘Q’."</p>
  
  <p>What do ‘B’, ‘D’, ‘W’, ‘M’, ‘A’, and ‘Q’ mean? I'm guessing that D is 'daily', W is 'weekly', M is 'monthly', A is 'annually', and that Q is 'quarterly', but I can't figure out what B is, and I can't find any documentation that confirms (or disconfirms) my guesses.</p>