Perhaps you should try some spelling variations:
"del factor" » "el factor", "model factor", "cell factor"
"d5 facto" » "de facto", "5 facto", "15 factor"
"e factor" » "e factors", "one factor", "age factor", "de factor", "e factr", "5 factor"
"ex facto" » "sex factor", "ix factor", "de facto"
"e facto" » "de facto", "e fact", "5 facto"
"de fact" » "de facto", "de fait", "e fact"

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: (((((("d5 facto") OR ("del factor"))) OR ((((("e facto") OR ("e factor"))) OR ("ex facto"))))) OR ("de fact")).
• Removing quotes may allow a broader search: (((((( d5 facto ) or ( del factor ))) or ((((( e facto ) or ( e factor ))) or ( ex facto ))))) or ( de fact )).
• Adding a wildcard symbol may retrieve word variants: (((((("d5 facto") or ("del factor"))) or ((((("e facto") or ("e factor"))) or ("ex facto"))))) or ("de fact"))*.