i think this points out that it is hard to really give good responses sometimes when all the details are not known ... in this case, we really don't have sufficient information on HOW samples were selected and assigned, METHODS and orders that items were heated and then porcelain applied, and on and on
for it to be totally randomized, we would have to have something akin to ... having 72 samples ... assigning them to temp and porcelain type first ... then executing this "design" in that order ... could be that sample 1 got 430 degrees and type b, sample 2 might have gotten temp 700 with porcelain type b, and so on but, we probably know that is NOT what happened ... because that would have created implementation problems we know in factories ... there are runs of different items at different times ... they might have a run of X from 8AM to NOON, then there is a transition period before Y gets done from 1PM to 5PM ... in this instance, it probably was the case that all 24 were heated to the first temp ... then when that was all done, the oven was revved up to the next higher temp and then the next 24 were heated ... and a final heat up to the last temp saw the final 24 done so, this is not exactly a totally randomized plan ... since there could have been some systematic difference from one batch to the other we also don't know how the porcelain was applied ... it might have been that after all were heated to temp 1 ... then the first 12 that came out of the oven were given porcelain type A ... since this was easier to do ... then the last 12 got (after the change over) porcelain type B if either temp or type of porcelain made a BIG difference, these procedural details probably don't make a hill of beans of difference but, of course, if the impacts (though maybe real) were very small, then some systematic error might make a difference as i said ... we just don't know however, i think trying to give the "design" the proper NAME is really not that important ... the real important matter is whether the implementation of the plan was sufficiently close enough to a fully randomized design that ... an analysis according to that design would be satisfactory in this case bottom line is: snippets of information given to the list ... does not necessarily allow us to field the ensuing inquiries ... and, it is better to probe more about methods and procedures first ... then to rush off with some analysis conclusion BUT WE DO IT ANYWAY! >If the samples have been treated independently, that is each sample is >individually raised to the randomly assigned temperature and >subsequently treated with the assigned porcelain type, the design is a >completely randomized design. Any application effects (including >possible deviations of supposed temperatures and irregularities during >the whole proces of heating and subsequent cooling) will contribute to >the random error of the observations. But when all samples of the same >temperature treatment are simultaneously put in the furnace and >treated as one batch the situation is different. In that case >application effects (whose existence and magnitude is not known >generally) are confounded with the effects of the temperature >treatment. In my comment I supposed and stated that probably this was >the situation at hand. I have to admit that the original message is >not entirely clear on this point. ============================================================== dennis roberts, penn state university educational psychology, 8148632401 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/ =================================================================
