**A/B Testing need-to-know terms**

The data science behind A/B testing can get complex pretty quickly. But, we’ve highlighted a few need-to-know terms to start with the basics.

**Null hypothesis **

The null hypothesis, or H0, posits that there is no difference between two variables. In A/B testing, the null hypothesis would assume that changing one variable on a web page (or marketing asset) *would have no impact* on user behavior.

**Alternative hypothesis **

On the flip side, an alternative hypothesis suggests the opposite of the null hypothesis: that changing an element *will* impact user behavior. Take the example below:

**Null hypothesis:** The size of a call-to-action button does not impact click rates.

**Alternative hypothesis:** Larger call-to-actions buttons result in higher click rates.

**Statistical significance**

Statistical significance is meant to signify that the results of an A/B test **are not **due to chance (rejecting the null hypothesis).

This is calculated by measuring the p-value, or probability value. So, if the p-value is low, it is saying that it’s *unlikely *the results of the A/B test were random.

A rule of thumb tends to be that when the p-value is 5% or lower, the A/B test is statistically significant.

**Confidence level**

Think of the confidence level as the inverse of the p-value. The confidence level is the indication of how likely it is that the results of your experiment are due to the changed variable (that is, these results are not random or a fluke occurrence).

If a test is considered statistically significant when the p-value is at 5%, then the confidence level would be 95%.