Unifying example for censoring & truncation

[RaphaelS1]

Probably add to intro.

e.g., looking at covid exposure & symptoms

1. Right-censoring: Exposure trial looking at time to disease. Right-censored if no disease.
2. Right-trunction: Retrospective study. Exposure time unknown, incubation times differ. People only included in study if they show symptoms. Right-truncated if patients with disease are unknown because long incubation (show symptoms after dataset end time). Data biased towards patients with shorter incubation times.
3. Left-censoring: TBD
4. Left-truncation: Time from exposure to symptoms is studied in COVID patients but some may die before symptoms are reported and are left-truncated as they can't enter the study after death; exposure times will therefore be slightly biased towards longer periods