Fig. 2From: Development of an algorithm for determining smoking status and behaviour over the life course from UK electronic primary care recordsDerivation of smoking status categories. This represents a single person through time. The top row (NEVER_SMOKER) shows the first and last dates as the start and end of the green bar. The second row (EX_SMOKER) shows the first and last dates as the start and end of the yellow bar. The third row (SMOKER) shows the first and last dates as the start and end of the red barBack to article page