How many Impressions or Clicks is enough to judge an ad's CTR?

[bigdealioo]

THANKS!...............

[yonnermark]

if you only have 100 impressions per day but view those stats over a week I'd say that's pretty reliable. But obviously higher numbers bring more reliable conclusions.

[Pengi]

you need to accumulate sufficient clicks to be significant - however many inmpressions that needs - 100 impressions and no clicks tells you little, 100 impressions and 50 clicks would be quite meaningful.

Look at how your number of clicks varies from day to day - I'd suggest you need about 10 times the average to get a decent estimate.

The content network can have some very dramatic effects on CTR for short periods though - possibly increasing impressions by more than 3 orders of magnitude but with much much lower CTR.