In my day, public information films were about the Green Cross Man and the fairy godmother saying "Learn to swim, young man, learn to swim!" Times have changed and now children as youndg as three are bing shown Nick "Oscar" Latimer's new production:
I am a massive fan of any way in which we eeconomists can make our point other than through slabs of text and I am delighted Nick gave permission to paste the link, thank you. The conversation between the rabbit and the dog does stir uncomfortable memories of a few meetings with pharma companies though ...
For what it's worth, I endorse the rabbit's view - the economics model in an HTA submission should test out several different ways of extrapolating the data and present statistics such as 'goodness-of-fit' plus graphs showing observed data versus plotted extrapolations for visual inspection. I have seen submissions where companies have argued only one form of extrapolation is appropriate but in general I would say it is best to use the rabbit's approach in the base case and then make any 'special case' in the sensitivity analysis.