Course Content

Probability Theory Mastering

1. Additional Statements From The Probability Theory

Course Overview Absolutely Continuous and Discrete Random Variables Cumulative Distribution Functions and Probability Density Functions Characteristics of Random Variables Random Vectors Useful Properties of the Gaussian Distribution Challenge: Detecting Outliers Using 3-Sigma Rule

2. The Limit Theorems of Probability Theory

Law of Large Numbers Law of Large Numbers for Bernoulli Process Challenge: Estimate Mean Value Using Law of Large Numbers Central Limit Theorem Challenge: Application of the CLT to Solving Real Problem

3. Estimation of Population Parameters

General population. Samples. Population parameters.Momentum estimation. Maximum Likelihood Estimation Challenge: Estimate Parameters of Chi-square Distribution Unbiased Estimation Challenge: Checking Bias of An Estimation Using Simulation Consistent Estimation Efficient Estimation Confidence Intervals for Population Parameters Challenge: Confidence Interval for Exponential Distribution Parameter

4. Testing of Statistical Hypotheses

What is Statistic Hypothesis? Type 1 and Type 2 Errors What is P-value?Comparing Means of Two Different Datasets Challenge: Using CLT to Compare Mean Values of Non-Gaussian Datasets Challenge: Resampling Approach to Compare Mean Values of the Datasets Testing the Hypothesis of Independence of Two Random Variables

Consistent Estimation

In statistics, a consistent estimation is an estimation that converges to the true value of the parameter as the sample size increases, meaning that the estimation becomes more and more accurate as more data is collected. Formally it can be described as follows:

This definition may seem rather complicated. In addition, in practice, it is not always easy to check the consistency of an estimate in this way, that is why we will introduce a simpler applied criterion of consistency:

Thus, if our estimator is asymptotically unbiased or simply unbiased and the estimator's variance decreases with increasing sample size, then such an estimator is consistent.

Let's show that the estimates of the sample mean and adjusted sample variance are consistent.

Sample mean estimation

The sample mean estimation is consistent by definition due to the law of large numbers: the more terms we include to calculate mean value, the closer the resulting value tends to the mathematical expectation.

Adjusted sample variance estimation

To check the consistency of adjusted sample variance let's use simulation:


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import numpy as np
import matplotlib.pyplot as plt

# Generate 5000 samples from a normal distribution with mean 2 and standard deviation 2
samples = np.random.normal(2, 2, 5000)

# Function to calculate adjusted variance of subsamples
def adjusted_variance_value(data, subsample_size):
    return samples[:subsample_size].var(ddof=1)  # Calculate the adjusted variance using Bessel's correction

# Visualizing the results
x = np.arange(2, 5000)  # Generate values for the number of elements to calculate variance
y = np.zeros(4998)  # Initialize an array to store the calculated variances
for i in range(4998):  # Loop through the range of subsample sizes
    y[i] = adjusted_variance_value(samples, x[i])  # Calculate adjusted variance for each subsample size

# Plotting the results
plt.plot(x, y, label='Estimated adjusted variance')  # Plot estimated adjusted variance
plt.xlabel('Number of elements to calculate variance')  # Set x-axis label
plt.ylabel('Variance')  # Set y-axis label
plt.axhline(y=4, color='k', label='Real variance')  # Add a horizontal line representing the real variance
plt.legend()  # Add legend to the plot
plt.show()  # Display the result

According to the visualization, we can see that as the number of elements increases, the adjusted sample variance tends to its real value, so the estimate is consistent.

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Section 3. Chapter 6