TSA is bad at data collection and that makes it hard to judge its performance

The Salt Lake Tribune found huge holes in TSA data that raise questions about the information’s value in charting the effectiveness of airport security. For example, TSA stopped counting confiscated firearms for three years. In 2008, it quit counting eight of 13 major categories of banned items, including knives, ammunition and box cutters (the weapon used by 9/11 terrorists).

The hit-and-miss data show TSA does not know how many total prohibited items are surrendered, so it cannot accurately track rates of such activity nationwide or at specific airports...Some security experts say such holes and variances make the database a poor tool to gauge TSA performance.

TSA Security Items Surrendered by The Salt Lake Tribune