Right, look at my phrasing:
Islam is adopted by many of those that have lost hope (prisoners, debtors, beggars, people in crises eg. Michael Jackson and so on).
I know myself that it cannot be quantified. I use Islam as an example here. Read the last sentence:
People see light only when they're in trouble.
Examples in Popular Culture are characters like John Abruzzi from Prison Break, though it's Christianity in his case.