Instructions: Given a passage with a question and an answer to that question, classify if the answer actually answers the question into 'yes' or 'no'. Output 'yes' if the answer answers the question and output 'no' if the answer does not answer the question.
Input: Question: Is directional distribution of neoplasia in Barrett 's esophagus influenced by distance from the gastroesophageal junction?
Answer: Single-center study may limit external validity.
Output:
no