Statistics & Probability5 min read
What a P-Value Is, and What It Is Not
A p-value is the chance of a result at least this extreme if the null hypothesis is true. A two-sided z of 1.96 gives p ≈ 0.050; here is how to read it.
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22 articles
- Statistics & Probability5 min read
Pearson Correlation: Calculate r Step by Step
Pearson's r ranges from −1 to +1. For x = 1…5 and y = 2, 1, 4, 3, 5 the sum-of-products method gives r = 0.80. See the steps and an outlier trap.
- Statistics & Probability4 min read
How to Read a Percentile (and Find the 50th)
A percentile is a position, not a score. See how the nearest-rank method finds the 50th percentile of 20 marks (69) and how it differs from a percentage.
- Statistics & Probability5 min read
Probability Basics: Favourable Over Total Outcomes
Probability is favourable outcomes divided by total equally likely outcomes: rolling a 5 on a fair die is 1/6, or 16.7%. Plus AND, OR and complement rules.
- Statistics & Probability5 min read
How to Find Quartiles and the IQR
Q1, Q3 and the IQR explained with a 12-value set: Q1 = 12.5, Q3 = 25, IQR = 12.5, and the 1.5 × IQR fences flag 58 as an outlier.
- Statistics & Probability4 min read
Sample Size for a Survey: How Many Responses?
A 95% confidence level and a ±5% margin need about 385 responses for a large population. See the formula and how a smaller population shrinks that.
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