Dr David Grimes, from Oxford University, devised an equation to express this, and then applied it to four famous collusions.
The equation developed by Dr Grimes, a post-doctoral physicist at Oxford, relied upon three factors: the number of conspirators involved, the amount of time that has passed, and the intrinsic probability of a conspiracy failing.
He then applied his equation to four famous conspiracy theories: The belief that the Moon landing was faked, the belief that climate change is a fraud, the belief that vaccines cause autism, and the belief that pharmaceutical companies have suppressed a cure for cancer.
Dr Grimes's analysis suggests that if these four conspiracies were real, most are very likely to have been revealed as such by now.