Define market-only rider experience metrics

Design rider experience metrics that are purely market-driven for a rides marketplace, where "experience" should capture supply–demand conditions rather than app interface or vehicle condition. Put forward a set of metrics—for example, 5-minute request fill rate, time-to-match, ETA quoted at request time, actual pickup wait, rider wait-hazard, and a price-adjusted wait index—along with one composite Market Balance Index that has an explicit formula and assigned weights. Give exact definitions, sampling windows, censoring rules for requests that are never fulfilled, holiday/outage exclusions, and a backtest demonstrating that the index responds to supply/demand shocks but not to UI releases.

Overview: This question assesses a data scientist's ability to design market-only rider experience metrics and a composite Market Balance Index, covering marketplace metric specification, survival/hazard modeling, price-adjusted indexing, censoring and normalization rules, and experimental backtesting with server-side logs.