What is the percentage change in the weighted average basic common shares outstanding between 2018 and 2019?
{"Weighted average common shares outstanding": {"2019 Basic": 597961.0, "2018 Basic": 660925.0}, "Net income available to common shareholders": {"2019 Basic": 3202943.0, "2018 Basic": 3614610.0}, "Net earnings per share available to common shareholders": {"2019 Basic": 5.36, "2018 Basic": 5.47}}
weighted_average_common_shares_outstanding_2019_Basic = df["Weighted average common shares outstanding"]["2019 Basic"]
weighted_average_common_shares_outstanding_2018_Basic = df["Weighted average common shares outstanding"]["2018 Basic"]
answer = (weighted_average_common_shares_outstanding_2019_Basic - weighted_average_common_shares_outstanding_2018_Basic) / weighted_average_common_shares_outstanding_2018_Basic * 100.0