Cycle helmet debate/Terms

Here are some of the terms and rhetorical devices you'll see in the cycle helmet debate both here and elsewhere.

Evidence
There are several classes of evidence.
 * longitudinal study and prospective study are terms used more or less interchangeably to describe a research study that involves repeated observations of the same population over a period of time. Longitudinal studies are used in medicine to suggest predictors of certain diseases. See also 
 * An observational study is a study designed to draw inferences about the possible effect of an intervention, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator. See also 
 * A cross-sectional study involves observation of some subset of a population at one time, as opposed to a longitudinal study which observes over a period of time. See also 
 * A time series is a sequence of data points, measured typically at successive times, spaced at (often uniform) time intervals. Plotting the head injury rates of a population over time yields a time series. See also 

People
Several rhetorical terms are used to refer to people in the helmet debate.
 * Helmet zealots are those who promote helmets with a religious zeal; these are the people who are responsible for helmet laws.
 * Anti-helmet zealot (AHZ) is a term coined by a Usenet troll, (probably Steven M. Scharf here) to undermine sceptical evidence.  To a good first approximation there is no such thing as an anti-helmet zealot, no laws forbidding the use of cycle helmets have yet been proposed.  The closest term with a basis in reality might be an anti helmet-zealot activist, one who actively opposes helmet zealots.
 * A True Believer is one who is completely convinced that helmets are an unalloyed good, and will never be persuaded otherwise by any amount of evidence. For them, it is essentially a religious issue.  True Believers are the kind of people who call a sceptic an anti-helmet zealot.
 * A liddite is one who lives in the past - 1989 to be precise.
 * A helmet sceptic is sceptical of helmet promotion. Most helmet sceptics are less sceptical of the confounding evidence, although this is partly because it is based on larger data sets.

Terms for helmets

 * Magic hat - so called because of their apparent ability to prevent all injuries even from sources clearly well outside their specified capabilities.
 * Polystyrene foam deflector beanie or PFDB, an allusion to the aluminium foil deflector beanie
 * Plastic prophyalactic, Plastic hat, foam hat
 * Martlehat, coined during the debate on the Martlew Bill, possibly by John B, who created the rather natty picture at right.