Python ## How to Calculate Correlation between Stock Price Movements with Python

In this lesson we will learn about **correlation** of assets, calculations of **correlation**, and **risk** and **coherence**.

The learning objectives of this tutorial.

- What is
**correlation**and how to use it - Calculate
**correlation** - Find
**negatively correlated**assets

**Correlation** is a statistic that measures the degree to which two variables move in relation to each other. **Correlation** measures association, but doesn’t show if x causes y or vice versa.

The correlation between two stocks is a number form -1 to 1 (both inclusive).

- A positive correlation means, when stock x goes up, we expect stock y to go up, and opposite.
- A negative correlation means, when stock x goes up, we expect stock y to go down, and opposite.
- A zero correlation, we cannot say anything in relation to each other.

The formula for calculating the correlation is quite a mouthful.

Luckily, the **DataFrames** can calculate it for us. Hence, we do not need to master how to do it.

Let’s get started. First, we need to load some time series of historic stock prices.

See this tutorial on how to work with portfolios.

```
import pandas as pd
import pandas_datareader as pdr
import datetime as dt
import numpy as np
tickers = ['AAPL', 'TWTR', 'IBM', 'MSFT']
start = dt.datetime(2020, 1, 1)
data = pdr.get_data_yahoo(tickers, start)
data = data['Adj Close']
log_returns = np.log(data/data.shift())
```

Where we also calculate the log returns.

The correlation can be calculated as follows.

```
log_returns.corr()
```

That was easy, right? Remember we do it on the log returns to keep it on the same range.

```
Symbols AAPL TWTR IBM MSFT
Symbols
AAPL 1.000000 0.531973 0.518204 0.829547
TWTR 0.531973 1.000000 0.386493 0.563909
IBM 0.518204 0.386493 1.000000 0.583205
MSFT 0.829547 0.563909 0.583205 1.000000
```

We identify, that the correlation on the diagonal is 1.0. This is obvious, since the diagonal shows the correlation between itself (AAPL and AAPL, and so forth).

Other than that, we can conclude that AAPL and MSFT are correlated the most.

Let’s add the S&P 500 to our **DataFrame**.

```
sp500 = pdr.get_data_yahoo("^GSPC", start)
log_returns['SP500'] = np.log(sp500['Adj Close']/sp500['Adj Close'].shift())
log_returns.corr()
```

Resulting in this.

Where we see that AAPL and MSFT are mostly correlated to S&P 500 index. This is not surprising, as they are a big part of the weight of the market cap in the index.

We will add this helper function to help find correlations.

We are in particular interested in negative correlation here.

```
def test_correlation(ticker):
df = pdr.get_data_yahoo(ticker, start)
lr = log_returns.copy()
lr[ticker] = np.log(df['Adj Close']/df['Adj Close'].shift())
return lr.corr()
```

This can help us find assets with a negative correlation.

Now, let’s test.

```
test_correlation("TLT")
```

Resulting in this following.

The negative correlation we are looking for.

This can be visualized to get a better understanding as follows.

```
import matplotlib.pyplot as plt
%matplotlib notebook
def visualize_correlation(ticker1, ticker2):
df = pdr.get_data_yahoo([ticker1, ticker2], start)
df = df['Adj Close']
df = df/df.iloc[0]
fig, ax = plt.subplots()
df.plot(ax=ax)
```

With **visualize_correlation(“AAPL”, “TLT”)** we get.

Where we see, when AAPL goes down, the TLT goes up.

And if we look at **visualize_correlation(“^GSPC”, “TLT”)** (the S&P 500 index and TLT).

Would you like to get 12% in return of your investments?

D. A. Carter promises and shows how his simple investment strategy will deliver that in the book **The 12% Solution**. The book shows how to test this statement by using backtesting.

**Did Carter find a strategy that will consistently beat the market?**

Actually, it is not that hard to use Python to validate his calculations. But we can do better than that. If you want to work smarter than traditional investors then continue to read here.

This is part of a 2.5-hour full video course in 8 parts about Risk and Return.

If you are serious about learning **Python for Finance check out this course**.

- Learn
**Python for Finance**with pandas and NumPy. **21 hours**of video in over**180 lectures**.*“Excellent course for anyone trying to learn to code and invest.”*–**Lorenzo B**.

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