Statistics & Probability4 min read
Standard Error of the Mean: SD ÷ √n in Plain Terms
Standard error = sample SD ÷ √n. With SD 15 and 36 observations it is 2.5, and quadrupling the sample only halves it. See how it differs from SD.
The Calcylator Blog
Big ideas for
everyday numbers.
Practical guides, clear examples, and smarter ways to calculate.
Statistics & Probability guides
22 articles
- Statistics & Probability5 min read
T-Test Statistic Formula With a Worked Example
The one-sample t statistic is (mean − claimed mean) ÷ (SD ÷ √n). With mean 54, claim 50, SD 10 and n = 25, t = 2.0 on 24 degrees of freedom.
- Statistics & Probability6 min read
Variance and Standard Deviation: n vs n−1
Population variance divides by n, sample variance by n − 1. See both on the same six numbers: 2.92 versus 3.5, and SD 1.71 versus 1.87.
- Statistics & Probability5 min read
Z-Score Formula: Standard Deviations From the Mean
A z-score subtracts the mean and divides by the standard deviation: (85 − 70) ÷ 10 = 1.5. That puts the value about the 93rd percentile if scores are normal.
Put what you learn into practice.
Explore our free calculators and apply these concepts to your own numbers.