Yeah, but that's not how you measure the success or otherwise of such schemes...

From The Daily Mail:

A council spent £134,000 employing a team of 22 'dog mess' wardens - but issued just 26 fines in three months.

Each ticket cost Islington Council, in north London, which ran the scheme, the equivalent of a staggering £5,150 to issue. The money was spent employing the wardens to pound the streets over a 12-week long pilot project, which the council hoped would be 'self-financing'. But it raised just £2,080.

Indignant outrage ensues, but that's not the point. The number of fines issued is almost completely irrelevant. The correct way of looking at it is:

i. Ascribe some sort of monetary notional cost to each dog shit on the pavement approx. equal to the unhappiness it causes people who have to walk past/through it plus cost of cleaning it up. This is very tricky - is it £10 or £20 or £1,000 per dog shit?

ii. Count the number of dog shits prior to the scheme being introduced.

iii. Announce with a great fanfare that the council means business, that it was have an army of pooper snoopers spying from every corner with the power to impose large fines for transgression.

iv. Count the number of dog shits for the period thereafter and subtract this from the number there were beforehand.

v. The cost-benefit analysis is then
cost = actual cash cost of scheme minus income from fines
benefit = reduction in number of dog shits multipled by notional cost of each.

As it happens, the scheme appears to have failed anyway, separate topic.

Imagine: a police force is so good at apprehending perp's that nobody ever dares commit a crime and no fines or punishments are ever imposed. Does this mean that that police force is a waste of money?