Question

What information does a target cost-per-acquisition (cpa) bid strategy need in order to find the optimal cost-per-click (cpc) bid for an ad each time it's eligible to appear?

Answer 1

They would need historical conversion data because using this allows you to find the optimal equivalent bid each time your ad is eligible to appear.  Even though you pay per click, you don't need to continuously adjust the bid to reach your conversion target