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# Which criteria does Marketo use to divide the audience into A and B?

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## Which criteria does Marketo use to divide the audience into A and B?

I've done an A/B  test using the whole email variation test type with an audience of 3000 people. The A/B test was done on everyone (I’ve selected 100% thus I haven’t selected any winner criteria). So far 1 email got 45% more opens than the other (that’s about 60 people). I’m confused because the subject and preview text are the same… the low opens one even had slightly more delivered (10+ people) than the other one.

The audience for the test is big enough to make a statistically significant conclusion that the subject line or/and preview text in As is much better than in B however it’s not the case since both are the same.

Any idea why that would happen?

Which criteria does Marketo use to divide the audience into A and B?

How Marketo makes sure that audience A has the same attributes as the audience B?

I feel like Marketo didn’t divide the audiences “fairly”

My issue now is how can I rely on Marketo to run the A/B test for us?

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Level 10 - Community Moderator

## Re: Which criteria does Marketo use to divide the audience into A and B?

The audience for the test is big enough to make a statistically significant conclusion that the subject line or/and preview text in As is much better than in B however it’s not the case since both are the same.

The distribution is random, there's not expected to be any clustering/unclustering by attribute values.

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Level 10 - Community Moderator

## Re: Which criteria does Marketo use to divide the audience into A and B?

The audience for the test is big enough to make a statistically significant conclusion that the subject line or/and preview text in As is much better than in B however it’s not the case since both are the same.

The distribution is random, there's not expected to be any clustering/unclustering by attribute values.

Level 2

## Re: Which criteria does Marketo use to divide the audience into A and B?

Knowing this how do you run A/B tests in Marketo to produce accurate results?

Level 10 - Community Moderator

## Re: Which criteria does Marketo use to divide the audience into A and B?

"accurate" is too vague, exactly what distribution algorithm are you expecting?

Level 2

## Re: Which criteria does Marketo use to divide the audience into A and B?

Most actions affect one group of our users more than others. So when we run A/B tests we want to make sure that the 2 groups are roughly equivalent so the differences in their behavior can be attributed.

If you're asking which specific distribution (binomial, normal, t- distribution, Chi-Square, etc) we want... then unfortunately I don't have the answer to that.

Do you know which distribution is used by Marketo for A/B tests?

Level 10 - Community Moderator

## Re: Which criteria does Marketo use to divide the audience into A and B?

Most actions affect one group of our users more than others. So when we run A/B tests we want to make sure that the 2 groups are roughly equivalent so the differences in their behavior can be attributed.

If you're asking which specific distribution (binomial, normal, t- distribution, Chi-Square, etc) we want... then unfortunately I don't the answer to that.

Do you know which distribution is used by Marketo for A/B tests?

Think you're overthinking it. It's equivalent to randomly shuffling the set using a (P)RNG, then slicing into 2 subsets — i.e. based on uniform distribution. There may be slight bias introduced by the exact implementation (i.e. crypto hash vs. RNG) but I strongly doubt that's causing what you're seeing.

Level 2

## Re: Which criteria does Marketo use to divide the audience into A and B?

I'm pretty sure I know what's the issue. One variation which had a gif went mostly to the promo/others tab..or maybe even the spam folder where the other went to the primary inbox that's why such a big gap in open rates though the subject and preview texts are the same.

Level 10 - Community Moderator

## Re: Which criteria does Marketo use to divide the audience into A and B?

Makes sense. You're always implicitly testing deliverability & inboxing alongside user engagement.