Table 1.

Contingency table comparing filter to ‘reference set’ and explanation of statistical descriptions

Filter	Manual review of each article
	Paramedic articles	Non-paramedic articles
Article identified	a	b	a + b
Article not identified	c	d	c + d
	a + c	b + d	a + b + c + d

Caption: Sensitivity = a/(a + c): proportion of all articles relevant to paramedics in the reference set that are retrieved by the filter. Specificity = d/(b + d): proportion of all articles not relevant to paramedics in the reference set that are correctly not retrieved by the filter. Precision = a/(a + b). NNR = 1/precision: the number of relevant and non-relevant articles that need to be screened in order to find one of relevance