The evidence isn't perfect but the interpretation depends on ideology not the quality of evidence
The evident about e-cigs is far from perfect and some of it is biased and unclear. But I've finally realised why the debate on policy is so polarised.
There is plenty of room for debate about what the evidence says about safety and what it implies about policy. But the debate we are actually having isn't about the evidence at all as McKee and Capewell's response demonstrates. it is about which ideological position you start with.
McKee seems to start with the view (in not just this piece but in many others) that we must crusade against anything associated with the evil tobacco industry. If the industry likes it, we should oppose it. Other players in the debate (including that of Public Health England) adopt a more pragmatic position that the focus of tobacco policy should be harm reduction.
You don't actually need to look at the quality of evidence to know how it will be interpreted, you just need to know which camp the author is in.
The ideological position of fighting a crusade seems to lead to position where every weakness in a piece of evidence is interpreted as industry spin, conflict of interest or a damning fundamental flaw. All things not proved to be harmless should be opposed even if they clearly reduce harm dramatically compared to the alternative. The slightest hint of e-cigs being a gateway to tobacco use is proof that they are even if the clear weight of evidence suggest this effect is insignificant.
But ideology does not make a good basis for rational policy assessment. And it encourages exactly the same unscientific tactics as the evil tobacco industry adopted to try to deflect the evidence of harm when it first appeared. McKee et. al. demand absolute proof of safety and seek every possible piece of uncertainty and doubt on the existing studies. But their standard is a poor basis for health policy (harm reduction not absolute harmlessness is surely a better position) and exacerbating every flaw in studies is exactly how the evil industry tried to minimise the evidence of harm. Just because you are on the side of the angels doesn't mean this tactic is a sensible scientific way to build public health policy. Most crusades start with good intentions but lead to bad outcomes as the ideology comes to dominate the original goal.
A crusade against an evil enemy is a poor basis for deciding policy but seems to be becoming the norm in the debates about what we should do about e-cigs, alcohol and food. Rational thinkers will ignore the ideologues and stick with pragmatic harm reduction as a basis for public health policy.
Competing interests: User of e-cigaretttes, former smoker