Which statement is true regarding the LENGTH statement in SAS when merging datasets with variable name definitions?

The LENGTH statement in SAS is designed to explicitly define the length of character variables in a dataset. When merging datasets, if a variable has been defined with a certain length in one dataset and that same variable appears in another dataset, the LENGTH statement can affect how SAS interprets that variable's length during the merge process.

The correct understanding is that if the LENGTH statement is encountered after a variable has been defined, it will indeed establish a new length for that variable regardless of any prior definitions in the current data step. This means that previous length definitions will be replaced by the new ones provided in the LENGTH statement. Therefore, it accurately reflects the functionality of the LENGTH statement that it can override earlier definitions, supporting the conclusion that option A does not describe the behavior of the LENGTH statement correctly.

Additionally, the LENGTH statement applies specifically to character variables, not formats. Choice C incorrectly limits the statement to numeric variables, while choice D also misrepresents the LENGTH statement's purpose, as it does not deal with formats at all.

In summary, the correct interpretation of how the LENGTH statement functions under these circumstances is crucial, emphasizing that it can redefine the length of variables as specified in the statement.