Learn Risk Assessment: Volatility and Sharpe Ratio | Investment Metrics and Portfolio Analysis

Python for Investors

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Understanding risk is essential for any investor. Volatility is a primary measure of risk, representing how much a portfolio's returns fluctuate over time. A portfolio with high volatility experiences larger swings in value, while a portfolio with low volatility is more stable. However, risk is not just about how much returns move—it's also about how those returns compare to the risk taken. This is where the Sharpe Ratio comes in. The Sharpe Ratio is a popular metric that helps investors evaluate the risk-adjusted performance of a portfolio by comparing its excess return (over a risk-free rate) to its volatility.


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import numpy as np
import pandas as pd

# Simulated daily returns for a portfolio (as from previous examples)
portfolio_returns = pd.Series([0.001, 0.002, -0.0015, 0.0025, -0.0005, 0.0012, 0.0008])

# Calculate portfolio volatility (standard deviation of returns)
volatility = portfolio_returns.std()

print(f"Portfolio Volatility: {volatility:.4f}")

The Sharpe Ratio helps you understand how much excess return you receive for the extra volatility you endure by holding a riskier asset. The formula for the Sharpe Ratio is:

Sharpe Ratio = (Portfolio Return - Risk-Free Rate) / Portfolio Volatility

Here, the portfolio return is typically the average return over a period, the risk-free rate is the return of a theoretically riskless investment (such as U.S. Treasury bills), and portfolio volatility is the standard deviation of returns, as calculated above. A higher Sharpe Ratio means better risk-adjusted performance, indicating that the portfolio is providing more return per unit of risk.


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# Assume an annualized risk-free rate (e.g., 2% per year, converted to daily)
risk_free_rate_daily = 0.02 / 252

# Calculate mean daily portfolio return
mean_return = portfolio_returns.mean()

# Calculate Sharpe Ratio
sharpe_ratio = (mean_return - risk_free_rate_daily) / volatility

print(f"Sharpe Ratio: {sharpe_ratio:.2f}")

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Section 2. Chapter 2

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Section 2. Chapter 2

Risk Assessment: Volatility and Sharpe Ratio

1. What does a higher Sharpe Ratio indicate about a portfolio?

2. Why is volatility important for investors?

3. What is typically used as the risk-free rate in Sharpe Ratio calculations?