Perhaps you should try some spelling variations:
"pettersson decrease" » "patterson decrease" (Expand Search), "pettersson decreased" (Expand Search), "pettersson increase" (Expand Search)
"per decrease" » "per decreased" (Expand Search), "per increase" (Expand Search)
"peers decrease" » "peers decreased" (Expand Search), "peers increase" (Expand Search)
"mean decrease" » "mean decreased" (Expand Search), "mean increase" (Expand Search)

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"pettersson decrease\") OR (((\"per decrease\") OR (\"peers decrease\"))))) OR (\"mean decrease\"))~".
• Removing quotes may allow a broader search: (((( pettersson decrease ) OR ((( per decrease ) OR ( peers decrease ))))) OR ( mean decrease ))~.
• Adding a wildcard symbol may retrieve word variants: (((("pettersson decrease") OR ((("per decrease") OR ("peers decrease"))))) OR ("mean decrease"))*.