T-Test Calculator - Free Statistical Hypothesis Testing
T-Test Calculator
Test hypotheses about population means. Choose from one-sample, two-sample, or paired t-tests.
One-Sample T-Test
Test if a sample mean differs from a hypothesized population mean.
Test Results
t-Statistic
p-value
Degrees of Freedom
Confidence Interval
Data Visualization
Summary Statistics
Effect Size
How to use this calculator
📊 How to Use This Calculator
- Choose your test type: one-sample, two-sample, or paired
- Enter your data (one value per line or comma-separated)
- Set your hypotheses and significance level
- Click the button to perform the test
- Review results: p-value, confidence interval, and visualizations
📐 Understanding T-Tests
One-Sample T-Test
Tests if a sample mean differs from a hypothesized value.
Example: Is average height different from 170 cm?
Two-Sample T-Test
Compares means of two independent groups.
Example: Do males and females have different average scores?
Paired T-Test
Compares paired observations (before/after, matched pairs).
Example: Is there a difference before and after treatment?
🌟 Real-World Examples
Example 1: Quality Control
One-sample test: Machine should produce 100g items
Test if actual production differs from target
Example 2: A/B Testing
Two-sample test: Compare conversion rates
Test if design A performs better than design B
Example 3: Medical Study
Paired test: Blood pressure before/after medication
Test if treatment reduces blood pressure
💡 Pro Tips
- • Check assumptions: normality, independence, equal variances
- • Use Welch's t-test when variances are unequal
- • Paired tests are more powerful for related data
- • Consider effect size, not just p-value
- • Larger samples make tests more sensitive
- • Two-sided tests are more conservative
⚠️ Common Mistakes to Avoid
- • Don't use paired test for independent samples
- • Check for outliers - they affect t-tests
- • Don't ignore assumptions (especially normality)
- • p < 0.05 doesn't mean the effect is important
- • Multiple testing increases Type I error rate
- • Small samples may lack power to detect differences
About this calculator
Perform one-sample, two-sample, and paired t-tests. Calculate t-statistic, p-value, confidence intervals with visual comparisons.
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