P-value calculator

This p-value calculator determines p-values and Z-scores based on user input. By entering either a Z-score or a p-value (e.g., left-tail, right-tail, central probability between 0 and Z, etc.), it calculates corresponding probabilities and displays them instantly. It’s useful for statistical analysis, helping to interpret the significance of observed values in relation to a normal distribution.

Please note that if multiple values are entered, only the topmost non-empty input field is used to calculate and display the results.

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What is a p-value?

A p-value is a probability measure used in hypothesis testing to assess the strength of the evidence against a null hypothesis. It represents the likelihood of observing the test results, or something more extreme, under the assumption that the null hypothesis is true.

Key points on p-values:

1. Interpretation: A small p-value (typically ≤ 0.05) suggests strong evidence against the null hypothesis, indicating that the observed data is unlikely to occur if the null hypothesis were true. A high p-value (> 0.05) suggests weaker evidence, so we fail to reject the null hypothesis.
2. Calculation: P-values are calculated based on the distribution of the test statistic (like a Z-score or t-score). For example, for a Z-score, the p-value can be found by locating the area under the standard normal distribution curve that lies beyond the observed Z-score.
3. Types of p-values:
   • Left-tail: Measures the probability of a value being less than a given test statistic.
   • Right-tail: Measures the probability of a value being greater than a given test statistic.
   • Two-tailed: Measures the probability of a value falling at either extreme of the test statistic, commonly used in tests for both high and low deviations.

P-values are essential for determining statistical significance, guiding decisions about whether or not to reject a hypothesis based on observed data.