Cronbach alpha信頼性係数

cronbach.py

import pandas as pd

def cronbach_alpha(dataframe, columns):
    ''' dataframe: pandas dataframe
        columns: list of the dataframe column names
    '''
    var_sum = 0 
    tmp_df = pd.DataFrame(index=dataframe.index, columns=['total'])
    tmp_df = tmp_df.fillna(0)

    for col in columns:
        var_sum += dataframe[col].var(ddof=False)
        tmp_df['total'] += dataframe[col]
    
    total_var = tmp_df['total'].var(ddof=False)
    
    alpha = (len(columns) / (len(columns) - 1)) * (1 - (var_sum / total_var))
    return alpha