A/B Testing: p-value

Bao Tram Duong
2 min readNov 16

The p-value in A/B testing is a statistical measure that helps assess the evidence against a null hypothesis. A/B testing is a common experimental method used in fields such as marketing, product development, and healthcare to compare two versions (A and B) of a variable (e.g., a webpage, an advertisement, or a treatment) and determine which performs better. The p-value is a crucial component in interpreting the results of A/B tests.

I. Key Points about P-Value in A/B Testing:

1. Definition:

  • The p-value is the probability of observing the observed data or more extreme results when the null hypothesis is true.

2. Null Hypothesis (H0):

  • In A/B testing, the null hypothesis typically states that there is no statistically significant difference between the two groups (A and B), implying that any observed difference is due to random chance.

3. Alternative Hypothesis (H1):

  • The alternative hypothesis contradicts the null hypothesis and asserts that there is a significant difference between the groups.

4. Interpretation:

  • A small p-value (typically less than the chosen significance level, often 0.05) suggests that the observed data is unlikely under the assumption of the null hypothesis.
  • If the p-value is less than the significance level, the null hypothesis is rejected, indicating that the observed difference is statistically significant.

5. Decision Rule:

  • Common decision rules include:
  • If p-value < α (e.g., 0.05), reject the null hypothesis.
  • If p-value ≥ α, fail to reject the null hypothesis.

6. Statistical Significance:

  • A result is considered statistically significant if the p-value is below the significance level. This means that the observed difference is unlikely to be purely due to chance.

7. Not a Measure of Effect Size:

  • The p-value does not quantify the size or practical importance of the observed effect. It only indicates whether the observed effect is statistically significant.

II. Steps in A/B Testing with P-Value:

Bao Tram Duong