
#1




Gini index interpretation
So you have an auto book of business worth X amount of money and you have two models, one with a gini index of .42 and one with .44. People looking at those numbers think, we spent Y months working on this models for a measly .02?!?!
Is anyone here aware of a way to interpret this in terms of dollars? For example, could we say something like, .02 is equal to saving Z dollars in loss dollars a year for every P amount of premium?
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#2




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#3




First, what other measures of "performance" was looked at?
Gini Index is a good for assessing if one model is able to better differentiate "high" vs. "low" risks (assuming that your model is predicting insured losses). But I don't think you're going to find a good (direct) connection between the difference in the Gini Index and some monetary result since a lot depends on being able to get the needed rate for the higher risks and still be able to sell (i.e., get more) of the lower risk; and this will require looking at other mechanisms than the Gini Index.
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#4




If you are interested in the dollar effect of lift, you should at the Lorenz curve underlying the Gini index. Pick a point on the horizontal (% Premium) axis. The value on the vertical (% loss) will give the % of loss associated with the % of premium. If the % of loss is less than the % of premium, you should consider using the refined class plan. Consideration can include adverse selection, price elasticity and the cost of implementing the refined class plan.
You may want to see my Actuarial Review article on the “Value of Lift” https://www.casact.org/newsletter/in...iewart&id=5584 This was written before our work on the Gini Index. We move on to the Gini Index because we (ISO) did not want to get hung up on the above considerations. That being said, I think it is appropriate for companies to make those considerations. 
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