Guides that teach, not just tell
Each guide here takes one idea students trip over and walks it slowly: plain words first, then the formal definition, then a worked example with numbers small enough to check on your fingers. They pair with the calculators. Read the guide, then try the tool.
Choosing and running tests
Which Statistical Test Should You Use?
The decision table: question and data in, test out.
Hypothesis Testing: The 5 Steps
The whole procedure, run on one example.
Sampling Methods
Random, stratified, systematic and cluster sampling.
One-Sample t-Test Guide
The workhorse test, walked through.
Paired t-Test Guide
Differences first, then the test.
Independent-Samples t-Test Guide
Welch by default, and why.
t-Test vs z-Test
One question about sigma decides.
One-Way ANOVA Guide
F, sums of squares and post-hoc sense.
Two-Way ANOVA Guide
Interactions before main effects.
Foundations
Descriptive vs Inferential Statistics
Summarizing data in hand vs betting on a population.
Population vs Sample
The whole, the part, and why random matters.
Parameter vs Statistic
Greek letters, Latin letters, and the gap between them.
Types of Data
Nominal, ordinal, discrete and continuous.
Levels of Measurement
Stevens' ladder: nominal, ordinal, interval, ratio.
Centres, spread and the bell curve
Measures of Central Tendency
Mean, median and mode, and when each leads.
Mean vs Median
Which to use, judged on salary and house-price data.
What Is Standard Deviation?
A typical distance from the mean, built step by step.
Sample vs Population SD
N or n minus 1, and Bessel's correction.
The Normal Distribution, Explained
z-scores and the 68-95-99.7 rule, with examples.
Step-by-step methods
How to Find the Standard Deviation
Five steps, one example, n or n - 1 settled.
How to Calculate a Z-Score
Centre, scale, read the percentile.
How to Find a P-Value
Statistic, distribution, tail.
How to Find a Percentile
Position formula and interpolation.
How to Find the Median
Odd, even and skewed data.
How to Find Outliers
Tukey's fences, and what flags mean.
Reading inference honestly
What Is a P-Value?
The definition, and what it never meant.
What Is a Confidence Interval?
Coverage, width, and the standard misreadings.
What Is Statistical Significance?
Detectable is not the same as important.
Type I vs Type II Errors
False alarms, misses, alpha, beta and power.
Correlation vs Causation
Confounders, and what actually settles the question.