What operator is used to select observations that include a specified substring?

The operator used to select observations that include a specified substring is the CONTAINS operator. This operator is particularly useful in situations where you want to find records within a character variable that contain a certain subset of characters, regardless of their position within the variable.

When utilizing the CONTAINS operator, you can effectively filter data to find any instance where a specific substring appears within a larger string. This capability is essential for text analysis or when handling data with varying descriptions that may meet certain criteria.

Although other operators like the LIKE operator may seem relevant, the LIKE operator is primarily used in conjunction with pattern matching in SQL queries, often varying from the straightforward substring search that the CONTAINS operator provides. The IN operator is generally used for matching values in lists, and the SUBSTR operator is designed for extracting substrings rather than selecting observations based on the presence of a substring.

This specificity of the CONTAINS operator makes it the most suitable choice for the question asked.