Interview Query

Ad Raters: Part 2

Have you seen this question before?

Let’s say we use people to rate ads.

There are two types of raters. Random and independent from our point of view:

  • 80% of raters are careful and they rate an ad as good (60% chance) or bad (40% chance). 
  • 20% of raters are lazy and they rate every ad as good (100% chance).
  1. Suppose a rater rates just three ads, and rates them all as good. What’s probability the rater was lazy?

2. Suppose a rater sees NN ads and rates all of them as good. What happens to the probability the rater was lazy as NN tends to infinity?

3. Suppose we want to exclude lazy raters. Can you come up with a rule for classifying raters as careful or lazy?

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