Perhaps you should try some spelling variations:
imputation research » mutation research, reputation research, population research
option research » opinion research, action research, optics research
multi option » multi location, multi population, multi ratios
july 2012 » july 2013
july 2009 » july 2008, july 2007, july 2019

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( multiple imputation research : july 2012 ) or ( multi option research : july 2009 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( multiple imputation research : july 2012 ) OR ( multi option research : july 2009 )).
• Adding a wildcard symbol may retrieve word variants: (( multiple imputation research : july 2012 ) or ( multi option research : july 2009 ))*.