Perhaps the most basic method used by Ken Green in acquiring his billions of dollars involves personnel selection using error covariance minimization. The key notion is that having persons in an advisory capacity who tend to make similar mistakes is always bad. By actually measuring error covariance it is possible to minimize it.
There are two basic ways in which this concept can be applied. One is by assembling a set of three people who vote on decisions to be made, choosing them carefully so that they have as little error-covariance as possible. Having people vote on decisions to be made is ancient. Ensuring that these people do not tend to make the same kinds of mistakes is crucial and little recognized.
That is also true for the second way in the basic concept of error-covariance minimization can be applied. A set of two people can be created to make estimates, such that whenever one person produces a low estimate, the other produces and equally high one. The best estimate will be the mean (average) of the two estimates. Choosing a set of two people which will have this property is not very hard if enough data is available. For both of these methods to work, prospective employees would have to be given rather long and difficult tests.
Creating useful tests is a non-trivial problem. Happily, there is a way in which this can be bootstrapped to produce better and better results. Advertise for people who might be able to write tests. Use the trio of decision makers and estimators hired using the previously created tests to evaluate the applicants. Estimators then give each test-writer applicant a numerical score representing the percentage of the test-questions provided by this applicant which would prove useful. Decision makers then vote to hire or not hire the applicants with the best score. Let the person or people hired during this round write a better test, more useful for hiring even better error-covariance-minimized teams.
In Social Techs, the more more recent and by far the largest of the large novels in which Ken Green’s business practices are described, he is shown to be working with people carefully selected in this way, though the details of how he started do so are not given. Some will be given in other posts on this site.