Business Context

EmailBoost, a digital marketing agency, launched an A/B test on its latest email campaign to evaluate the effectiveness of a new subject line. The goal was to determine if the new subject line significantly increased the click-through rate (CTR) compared to the original.

Given Data

Task

Determine whether the observed 4.0 percentage point increase in CTR is statistically significant.

Requirements

1. State the null and alternative hypotheses.
2. Calculate the pooled proportion and standard error.
3. Compute the z-test statistic.
4. Find the p-value (two-tailed test).
5. Determine whether to reject H₀ at α = 0.05.
6. Interpret the results: should EmailBoost adopt the new subject line?

Assumptions

• Users were randomly assigned to control/treatment groups.
• Each user is counted only once (no repeat clicks).
• The test duration was sufficient to account for daily variations.