- High Value Action / Downstream Impact == using a "twins" comparison, estimate the 12-month impact of a customer taking a particular action (e.g. sign up for Prime, watch their first Prime Video, etc.), compared to one who doesn't. HVAs are basically those "A's" which turn out to have a high numeric DSI value.
- Downstream Expectation == similar but very different - instead of quantifying the impact of a single action, DSE tries to estimate the combined downstream causal impact of a user taking an initial action... there's a sophisticated methodology there that tries to strip away confounding factors like "rich people who would've shopped more anyways, are also naturally more likely to sign up for Prime", because they truly want to measure the causal benefit of Prime itself, separate from the fact that richer customers generally spend more no matter what
These are both long-term methodologies, that were explicitly designed in response to the problems of: short term experiments that didn't capture long-term negative effects, and different parts of Amazon having vastly different methodologies for measuring business impact (e.g. page views vs search impressions vs downloads vs orders vs whatever... no, everyone should optimize for the same customer level financial metric which is a flavor of growth-adjusted composite contribution profit (GCCP) that's partly derived from DSE)