= Solution
The birth-period comparison requires <consistency in causal inference>[consistency], no interference between individuals, and a real discontinuity in sugar exposure at the end of rationing. Near the cutoff, potential diabetes outcomes must otherwise vary continuously with birth date: no simultaneous policy, nutritional, diagnostic, seasonal, or demographic discontinuity may affect them. Birth dates must not be manipulable around the cutoff, and survival and UK Biobank participation must not create differential <selection bias>. These assumptions make cutoff assignment locally exchangeable and give a <regression discontinuity design> an exclusion restriction in which birth period affects diabetes through sugar exposure.
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