Asset ratings are distributed based on the number of impressions they receive in each ad group.

• The all conversion value they acquired over the last 30 days.
• The average click-through rate (CTR) they acquired over the last 30 days.
• The number of conversions they receive in each ad group.
• The number of impressions they receive in each ad group.

The correct answer is: The number of impressions they receive in each ad group.