Perhaps you should try some spelling variations:
travel surveys » travel survey, level surveys, travel success
level studies » legal studies, event studies, local studies
panel surveys » panel survey, phone surveys, level surveys
cold level » color level, word level, second level
re surveys » lek surveys, tie surveys, use surveys

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: harvard cold level studies ((re surveys) or (((panel surveys) OR (travel surveys)))).~.
• If you are trying to use Boolean operators, they must be ALL CAPS: harvard cold level studies ((re surveys) OR (((panel surveys) OR (travel surveys))))..
• The words AND, OR and NOT may confuse the search; try adding quotes: "harvard cold level studies ((re surveys) or (((panel surveys) OR (travel surveys)))).".
• Adding a wildcard symbol may retrieve word variants: harvard cold level studies ((re surveys) or (((panel surveys) OR (travel surveys)))).*.