def calculate_lives_improved(param_df):
    """Create a new column for lives improved in a df
       Inputs:
           param_df - a df of parameters must contain columns: 'lives_touched' and 'efficacy'
       Returns:
           a df with a lives_improved column added
    """
    param_df['lives_improved'] = (param_df['lives_touched']*param_df['efficacy'])
    return param_df