# How to check for correlation among continuous and categorical variables?

## Question:

I have a dataset including categorical variables(binary) and continuous variables. I’m trying to apply a linear regression model for predicting a continuous variable. Can someone please let me know how to check for correlation among the categorical variables and the continuous target variable.

Current Code:

```
import pandas as pd
df_hosp = pd.read_csv('C:UsersLAPPY-2DesktopLengthOfStay.csv')
data = df_hosp[['lengthofstay', 'male', 'female', 'dialysisrenalendstage', 'asthma',
'irondef', 'pneum', 'substancedependence',
'psychologicaldisordermajor', 'depress', 'psychother',
'fibrosisandother', 'malnutrition', 'hemo']]
print data.corr()
```

All of the variables apart from lengthofstay are categorical. Should this work?

## Answers:

Convert your categorical variable into dummy variables here and put your variable in numpy.array. For example:

**data.csv**:

```
age,size,color_head
4,50,black
9,100,blonde
12,120,brown
17,160,black
18,180,brown
```

Extract data:

```
import numpy as np
import pandas as pd
df = pd.read_csv('data.csv')
```

**df:**

Convert categorical variable `color_head`

into dummy variables:

```
df_dummies = pd.get_dummies(df['color_head'])
del df_dummies[df_dummies.columns[-1]]
df_new = pd.concat([df, df_dummies], axis=1)
del df_new['color_head']
```

**df_new:**

Put that in numpy array:

```
x = df_new.values
```

Compute the correlation:

```
correlation_matrix = np.corrcoef(x.T)
print(correlation_matrix)
```

Output:

```
array([[ 1. , 0.99574691, -0.23658011, -0.28975028],
[ 0.99574691, 1. , -0.30318496, -0.24026862],
[-0.23658011, -0.30318496, 1. , -0.40824829],
[-0.28975028, -0.24026862, -0.40824829, 1. ]])
```

See :

correlation in this scenario is quite misleading as we are comparing categorical variable with continuous variable

There is one more method to compute the correlation between continuous variable and dichotomic (having only 2 classes) variable, since this is also a categorical variable, we can use it for the correlation computation.

The link for point biserial correlation is given below.

https://www.statology.org/point-biserial-correlation-python/