1014 Journal of Economic Literature,Vol.XLII(December 2004 impr nnd that employs a standard subject pool of extent of discrimination in the sports-card marketplace. set of rules; an artefactual field experiment is the 3.Methodological Imp ortance of Field same as a conventional lab experime Experiment but with a nonstandard subject pool:1 a framed field experiment is the same as an artefactual field experiment but with Fieldpecause they mechanicologically ecause they mechanically f field context in either the co pay attention to issues tha great researcher seem task,or information set that the subiects to intuitively address.These issues cannot be comfortably can use. forgotten in the field,but they are of more ·a general importance. The goal of any evaluation method for "treatment effects"is to construct the prop- these task nere the subjects dokow er counterfactual,and economists have that they are in an experiment. rnative methods We recognize that any such taxonom of nstructing the counterfactual:co leaves gaps,and that certain studies may not fall neatly into our classification scheme trolled experir ments,natural (PSM) Moreover,it is often appropriate to con- nstr duct several types of experiments in order to nd t 3 identify the issue of interest.For example approache with treatme e y as the th ment.and le me w tho Harrison and List(2003)conducted artefac tual field experiments and framed field treated and eriments with the same subject pool.pr The treatment cisely to identify how well the he effect for unit i can then be measured as istics might naturally t=y-yo.The major problem,however,is the latte one of a missing counterfactual:t.is unknown It we could observe the outcome for an untreated observation had it been conducted ctual,fr and natur treated,then there is no evaluation problem experiments to investigate the nature and Controlled" experiments.which include laboratory experiments and field experi ments esent the most onvincing method of creating the counterfa al,sinc side trol group ents the popu field with We simplify by c the lo of peter Boh ontin of st albeit wit ics.one the Vicl might have some measure of risk ave ne pre run in which the ntrol cking-Reiley (2002