Fig. 1.

Conditions that lead to negative spillover. There are four conditions that lead to negative spillover, each of which concerns a different portion of the trial pathway. All these conditions relate to the presence of a scarce resource that represents a constraint on care delivery. The four conditions are (1) treatment and control arms draw from a shared resource pool, (2) the presence of a scarce resource in the trial setting (red circle), (3) the study intervention increases resource demand (thick blue arrow), and (4) resource utilization affects study outcomes (thin orange arrow on left, thick orange arrow on right)