[brudgers]

The conversion rate will tend to be low in any process that is designed to protect against false positives. Protecting against false positives is generally the preferred process for early stage companies and late stage companies (e.g. small startups and Google/Facebook etc.) A company that is staffing up fast can often exchange more churn for expansion, in part because even with a selective process the rapid change induced by expansion will cause churn organically as people's roles and responsibility evolve and the hierarchy adds layers and the org chart adds links.