def apply_diagnostic_inflation(cov_pop_burden_df, param_df, index):
    """Inflates the target_pop in df 
       Inputs:
           cov_pop_burden_df - a df with the column 'target_pop'
           param_df - a df of parameters, must contain the columns 'inflation_factor'
           index - a string that is one of the indexes of param_df
       Returns:
           a df with inflated target_pop column
    """
    new_cov_pop_burden_df = cov_pop_burden_df.copy()
    new_cov_pop_burden_df['target_pop'] = (new_cov_pop_burden_df['target_pop'] * 
                                           param_df.loc[index, 'inflation_factor'])
    return new_cov_pop_burden_df