A marketing team can afford to contact 10% of 50,000 customers. A gain chart shows that the top decile ranked by the model contains 38% of all eventual buyers, versus 10% for random selection.
What is the lift in the top decile, and what does it mean?
Why did you pick that answer? Two or three sentences. The act of articulating it is what builds the judgment — not the click that follows.
Lift is the ratio of the model's capture rate to random: 38% / 10% = 3.8. With a fixed contact budget, that ratio translates directly into revenue — the campaign reaches nearly four times the buyers it would by mailing at random. Gain and lift charts are the language of budget-constrained targeting, where the question is not "who is above 0.5?" but "who are the best 5,000?"
38 − 10 = 28 points is the gain over random, a valid number but not the lift, which is a ratio.
38% is the share of all buyers who are in the top decile, not the share of the decile who buy. Those are different denominators.
The 10% is the size of the contacted group, not a performance measure.