Lecture 1 summary · January 15, 2027
The decision and its information set
Complete chapter · Laboratory ch01 · Practice · All summaries
The economic question
Define an economic target and decision deadline before choosing a model. A low error cannot rescue information unavailable at the origin.
Central relation
Individual problem
Equally weighted temperatures are 40 and 80. Heating exposure is the positive part of 65 minus temperature. Compare transformation before and after averaging.
Worked reasoning
Average temperature is 60, so its heating exposure is 5. Average heating exposure is one half of 25, or 12.5. Nonlinear transformation does not commute with averaging.
A consequential failure
Observed target-month weather is quietly included in an earlier forecast.
Repair
Retain observation, release, vintage, origin, and target dates. Forecast an unavailable predictor or declare a scenario.