what if we see, from the side, one person on the right swing his/her fist ... and, as the fist arrives at what appears to be the impact point of the face of a person on the left ... that IMMEDIATELY the person on the left falls backwards and down
now, we do this over and over again ... and observe the same result we want to say that the impact to the FACE ... CAUSED the person on the left to fall down but, did it? in a sense, this is like a perfect correlation in that ... when the person swung to the RIGHT .. the person on the left NEVER fell backwards and down with an r = 1, karl would say that this has removed ALL extraneous factors from the possibility of an explanation for why the person fell ... or did not fall however, what is UNBEKNOWNST to the viewer ... there was a clear panel between the two people ... thrower of the punch and, the one on the left ... and, each time the person threw a punch ... and it LOOKED like the punch TO the person "caused" a fall down, ... in actuality there was an electronic triggering mechanism that ... when the panel was activated ... lead to some electrical shock being applied to the person on the left ... that made the person fall down it could be that if you viewed this from the angle of both people ... 90 degrees rotated ... you could see that there was a clear separation of 2 or more feet between where the punch hit the clear panel and ... where the face was leaning up against the panel so, the punch did NOT directly touch the face ... and in that sense, could not have caused the person to fall backwards and down even though these may be the "facts" ... the sideways view clearly has missed that there were OTHER things in the chain of events ... that LEAD to the person falling backwards and down r values ... even perfect ones ... are in an impossible statistical position to say anything about cause ... or, more importantly, what causes what the r that goes along with some manipulative procedure that varies X and produces some corresponding Y change ... is just a tag along statistic ... and may not really (even when perfect) suggest anything about HOW X, when manipulated, PRODUCED the Y change that we see ... thus, the use of r in this case as an index of how MUCH X CAUSES Y ... is a statistical stretch _________________________________________________________ dennis roberts, educational psychology, penn state university 208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED] http://roberts.ed.psu.edu/users/droberts/drober~1.htm ================================================================= Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =================================================================
