Please note, your implied definition of ârandomâ above is, wellâŚ strictly not random. Well, at least not in terms of determining *within each survey* whether or not to show this ârandomâ question. As defined - âof 10 households visited, 5 should show the questionâ - would require randomly picking a subset of 5 of the 10 *a priori*, and somehow communicating this pre-selected list to the device when filling in the 10 (and no more or no less) surveys. Picking a random number of 0 or 1 within each form will, **on average**, show the question 50% of the time, but thereâs no guarantee that it will only show up on exactly 5 of the 10 surveys, or even show up on any of them at all!

Strictly speaking there is nothing (statistically) preventing exactly this from happening (without either a priori determining the 5 of 10, or somehow checking all previous instances - which then makes it no longer ârandomâ).