Screening Effects of the National Health Screening Program on Developmental Disorders.

Sil et al. tracked Korea's national developmental-delay screening program for ten years. They looked at how many kids got screened and how many were missed.

The team counted false negatives — kids who really had delays but passed the screen. They also checked if age, income, or city size changed the miss rate.

Screening use rose at first, then dropped. More troubling, the miss rate climbed from about 3 in 100 kids to nearly 24 in 100.

Older children and families in poorer or rural areas were more likely to be missed.

Sim et al. (2015) saw the same problem in a smaller study. Their toddler tool also flagged too many kids who were actually fine — high false positives. Both papers show screening balance is hard.

Pandey et al. (2008) found the M-CHAT missed more ASD when used at 18 months versus 24 months. Sil’s national data echo this: older toddlers slipped through more often.

Bong et al. (2019) offer a bright spot. Their new Korean screener, BeDevel, kept sensitivity and specificity high in local toddlers. It shows better tools exist, but Korea’s national program has not adopted them yet.

If you screen toddlers, do not trust a single pass result, especially for kids over two or from rural families. Plan a second look or direct referral. Also, audit your own tool every year — false-negative drift can creep up just like it did in Korea.