The incidence of dementia for those aged 30-64 is about 54 per 100000. If you have a test that is 90% accurate and someone tests positive, according to Bayes you have 0.5% chance of actually having it.<p>Testing like that seems pointless to me.<p>Working: (0.9 * 0.00054) &#x2F; (0.9 * 0.00054 + 0.1 * 0.99946)