IPD reviews should be considered in circumstances where the published information does not permit a good quality review, or where particular types of analyses are required that are not feasible using standard approaches. There are situations where the IPD approach will not be feasible, because data have been destroyed or lost or, despite every effort, researchers do not wish to collaborate. There may also be circumstances where it may not be necessary, for example if all the required data are readily available in a suitable format within publications. Further details of when IPD many be beneficial are given in the Box 18.1.a.