whether there is a treatment or intervention (active) or not (passive). Active designs
include:
Randomised control trials (with or without blinds)
Quasi-experiments - including interrupted time series
Natural experiments
Action research
Design studies
and some might say
Participant observation.
Passive designs include:
Cohort studies (time series and retrospective)
Other longitudinal designs
Case-control studies
New political arithmetic
Cross-sectional studies
and some might say
Systematic reviews (including Bayesian)
The choice depends largely on the kind of claims and conclusions to be drawn, and to
a lesser extent on the practicalities of the situation and resources available. I say these
are lesser considerations because if it is not possible for financial, ethical or other
reasons to use a suitable design then the research should not be done at all (as
opposed to being done badly, and perhaps leading to inappropriate claims to
knowledge). The need for warranted conclusions requires the researcher to identify
the kind of claims to be made - such as descriptive, associative, correlational or
causal - and then ensure that the most appropriate possible design is used. Put
simply, a comparative claim must have an explicit and suitable comparator, for
example. The warranting principle is based on this consideration - if the claim to be
drawn from the evidence is not actually true then how else could the evidence be
explained? The claim should be the simplest explanation for the available evidence.