# Should the experiment goal be purchases or add-to-cart clicks?

Asked by Corinne Baptiste on 2024-07-23. Tags: ab-testing, goals, methodology.

Hello everyone. I am a CRO specialist at an agency and I keep having the same
debate with clients. They want "purchase" as the primary goal on every test,
including tests on category pages that sit five steps away from checkout. My
position is that the goal should sit closer to the element being tested, but I
would like to ground the advice in how Croct actually works.

Specifically: how does the choice of primary goal interact with the thresholds
an experiment must clear before it resolves? And is there a way to keep an eye
on the macro metric without making it the primary goal

## 2 answers

### Accepted answer from Anneke Visser (2024-07-23)

The thresholds themselves make the argument for putting the goal closer to
the tested element.

An experiment stays in progress until each variant reaches 1000 visitors and
25 conversions of the primary goal, over at least a week. The conversion
threshold is the one a distant macro goal punishes. If your category page
test uses purchase as the goal and only 1.5% of category visitors ever buy,
you need enormous traffic per variant before each one collects 25 purchases.
Worse, the signal is diluted: four other funnel steps sit between the tested
element and the goal, each adding noise that has nothing to do with your
change.

A micro goal close to the element, add-to-cart from that page, resolves much
faster because the conversion rate is higher and the causal chain is short.
The honest caveat to give clients is proxy risk: you can win the micro metric
while doing nothing for revenue.

The workable pattern is both. Set the micro conversion as the primary goal so
the experiment resolves in reasonable time, then use the results drill-down
by custom events to check the macro impact on the same participants. You get
a fast decision plus a sanity check that the proxy did not lie.

#### Reply from Corinne Baptiste (2024-07-24)

The 25-conversions-per-variant framing is exactly the concrete argument I
needed. Merci, this goes straight into my client onboarding deck.

### Answer from Karl J. (2024-07-25)

One practical note on setup: the primary Goal ID has to reference an event
that is already being tracked, you cannot point it at a metric that exists
only in your head. If the client store runs one of the commerce integrations,
events like orderPlaced and checkoutStarted are tracked automatically and the
conversion-indicating ones record a Goal Completed, so both the micro and
macro candidates are usually already available. Worth checking the event
stream before the goal debate, sometimes the event they want is not wired up
yet and that settles the discussion for the first test.