Are any of the following values outliers? 3 5 8 1 4 11 3 1 18

It appears that the only major outlier of this set of numbers could be is 18 but that is incorrect. The answer is none.

An outlier in a distribution is a number that is more than 1.5 times the length of the box away from either the lower or upper quartiles. Specifically, if a number is less than Q1 - 1.5*IQR or greater than Q3 + 1.5*IQR, then it is an outlier.

Basically 18 appears to be inside the box and so does 1

11 and 18, 18 if it's only one option