Perhaps you should try some spelling variations:
"operational research/decision theory" » "international research/decision theory"
"educational research/decision theory" » "education research/decision theory"

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("operational research/decision theory") OR ("operations research/decision theory"))) OR ("educational research/decision theory")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"operational research/decision theory\") OR (\"operations research/decision theory\"))) or (\"educational research/decision theory\"))".
• Removing quotes may allow a broader search: (((( operational research/decision theory ) OR ( operations research/decision theory ))) or ( educational research/decision theory )).
• Adding a wildcard symbol may retrieve word variants: (((("operational research/decision theory") OR ("operations research/decision theory"))) or ("educational research/decision theory"))*.