Measure fake account prevalence

A social platform is concerned about fake accounts. Leadership wants to understand how serious the problem is and whether a new detection model or enforcement policy should be launched. How would you approach this problem? In your answer, discuss: - how you would define a fake account operationally - how you would estimate prevalence and business impact - what metrics you would use to evaluate a detection system - how you would deal with class imbalance, delayed labels, and selection bias from user reports or manual reviews - how you would measure false-positive harm to legitimate users - how you would evaluate a new intervention online, given that attackers may adapt over time