And here is a link to Ron Clarke and Pat Mayhew's classic study on gas suicides in Britain - www.journals.uchicago.edu/doi/epdf/10....

Because some people aren’t trustworthy. I’ve come across machines on several occasions where the previous person has just done a runner. Random checking is a relatively efficient strategy (like random breath testing)

I confess I’ve not read any evaluations. Do you have a reference?

Please add me too

I already know how it ends

Mine have finally arrived

Yep it's in the ECCA book - both 1st and 2nd eds