How does the detection threshold affect true detections and false alarms?

How does the detection threshold affect true detections and false alarms?

• A. Lowering the threshold increases both true detections and false alarms; raising it reduces both.
• B. Lowering the threshold reduces false alarms.
• C. Changing threshold only affects true detections, not false alarms.
• D. Threshold does not affect system performance.

Answer: (C)

Setting the detection threshold defines how easily the system calls a signal present. If you lower the threshold, you’re more likely to declare a detection, so true detections increase but false alarms also rise because noise can trigger detections too. If you raise the threshold, you require stronger evidence before saying “target present,” so true detections fall and false alarms also fall. In short, changing the threshold affects both outcomes—the trade-off between catching real targets and avoiding false alarms is driven by where you set that threshold. The idea that only true detections change or that threshold doesn’t affect performance isn’t correct.

Setting the detection threshold defines how easily the system calls a signal present. If you lower the threshold, you’re more likely to declare a detection, so true detections increase but false alarms also rise because noise can trigger detections too. If you raise the threshold, you require stronger evidence before saying “target present,” so true detections fall and false alarms also fall. In short, changing the threshold affects both outcomes—the trade-off between catching real targets and avoiding false alarms is driven by where you set that threshold. The idea that only true detections change or that threshold doesn’t affect performance isn’t correct.