Investigations of heterogeneity
We have listed sources of heterogeneity that we investigated if adequate data were available in the Secondary objectives. In this version of the review, we used stratification to investigate heterogeneity as we considered it was inappropriate to combine studies. In future updates, if meta‐analysis becomes possible, we will investigate heterogeneity through meta‐regression.
We will stratify by reference standard and study design. In this version of the review we have stratified by study design only, as stratification by reference standard was not yet possible.