Pooled or Unpooled Variance t Tests and Confidence Intervals? (To Pool or not to Pool?) @jbstatistics

Pooled or Unpooled Variance t Tests and Confidence Intervals? (To Pool or not to Pool?) @jbstatistics

Uploaded June 2013 | Updated September 2026, 2 hours ago

I discuss the assumptions of both the pooled-variance and Welch (unpooled variance) t tests and confidence intervals, and their advantages and disadvantages. I illustrate some of pros and cons using the results of two simulations.

Pooled or Unpooled Variance t Tests and Confidence Intervals? (To Pool or not to Pool?)

Confidence Intervals for One Mean: Sigma Known (Z Method)

Type I Errors, Type II Errors, and the Power of the Test

Deriving the Mean and Variance of the Sample Mean

The Law of Total Probability

Confidence Intervals for One Mean: Determining the Required Sample Size

Inference for Two Means: Introduction

Simple Linear Regression: Inference on the Slope (The Formulas) (Old, fast version)

The Binomial Distribution: Mathematically Deriving the Mean and Variance

Proof that if events A and B are independent, so are Ac and B (and A and Bc)

Discrete Probability Distributions: The Poisson Distribution (STAT I – Full Lecture)

The Poisson Distribution: Introduction (fast version)

Pooled or Unpooled Variance t Tests and Confidence Intervals? (To Pool or not to Pool?)