Answer: Type 1 error
Explanation: Type 1 error exists when a researcher incorrectly rejects the null hypothesis. This means wrongly rejecting what is correct. This is different from. The type 2 error where the null hypothesis which is wrong is incorrectly accepted.
In the scenario above, it has already been established that half of the 500 children did have ADHD, However, result of the test says only 100 of the children have ADHD, thereby incorrectly identifying 150 children who actually did have ADHD has been free of ADHD. Thereby rejecting the null or established result.