What ProbLab is
ProbLab is an educational web tool built for students, teachers, analysts and anyone who needs to calculate probabilities, confidence intervals, sample sizes, hypothesis tests or A/B testing results without installing any software.
The goal is to combine interactive computation with clear explanation: every tool prioritizes visible formulas, assumptions, interpretation of results and applied examples.
Who is behind it
The project is maintained by Vicente Castellar. You can reach out for corrections, suggestions or improvement proposals at vic.sebastia@gmail.com.
ProbLab does not replace professional judgment or the methodological review of a study, but it offers a practical basis to check calculations and understand the usual statistical steps.
What you will find on the site
- Distribution calculators for PDF, CDF, tails and quantiles.
- Statistical tables with critical values and cumulative probabilities.
- Sample sizes for means, proportions and comparisons.
- Confidence intervals for estimates and uncertainty.
- Hypothesis tests for means, proportions, variances and goodness of fit.
- A/B testing tools for conversion, power, a Bayesian approach and simulation.
Recommended learning resources
Quality external sources for anyone who wants to learn statistics or double-check concepts:
- Khan Academy — Statistics and probability — free courses with interactive exercises, from basic concepts to inference.
- OpenIntro Statistics — freely available university-level statistics textbook, widely used in undergraduate courses.
- NIST/SEMATECH e-Handbook of Statistical Methods — official technical reference from the U.S. National Institute of Standards and Technology on applied statistical methods.
Transparency and improvements
The calculators are reviewed so that formulas, critical values and interpretations stay consistent. If you spot a discrepancy, report it together with the input case and the expected result so it can be reproduced.
See also the methodology page for the calculation criteria, rounding and limitations.