Without knowing the distribution of startups with 1, 2, 3, 4, 5+ etc founders, it's hard to tell how much more/less likely each group is to succeed.
Who cares if 12% of solo founders make a successful exit, vs 14% of two founder companies. If you are a lone wolf and want to work alone, you are going to fail if not alone. If you are a social thinker and hate working alone, you would be silly to form a solo startup.
It's simple.
But it may matter for investors looking at things with the opposite perspective - for example, is it a good/bad heuristic to ignore companies with 5+ founders?
I came here to say exactly this. The entire article appears to misunderstand conditional probability.
Though I agree, they should have at least addressed the fact, and admitted that their data was suggestive at best.
And accounting for co-founder relationships and role changes is also hard, which happens often as a startup grows.
If 99.9% of all startups have 1 founder then the numbers for everything except 1 founder startups look incredible.
It's not very reliable, and it may not generalize well. But it's something.