Let me take a (somewhat) contrarian position to those previously expressed. An experiment is any test of a hypothesis. An experiment can involve the use of observational (unmanipulated) data, as long as the hypothesis is clearly stated prior to the collection of the data. While it is true that an experiment involving manipulation can provide some of the best evidence for causal relationships, causal relationships can be deduced from observation data combined with other information about how the world works.
All of that said, the situation described below is what I would call a hypothesis-generating activity. That is, you want to look for a potential correlation that you will use to then test specific mechanisms (i.e., doex chemical X kill fish?). It would be a hypothesis-testing activity, if you had a prespecified hypothesis concerning a particular pollutant that previous experiments have shown to kill or otherwise harm fish. Sam Scheiner Voltolini wrote: > > Hi, > > I was reading a definition of "experiment" in science to be used in a > lecture and the use of treatments and controls are an important feature of > an experiment but.... my doubt is... is it possible to plan an experiment > without a control and call this as an "experiment" ? > > For example, in a polluted river basin there is a gradient of contamination > and someone are interested in to compare the fish diversity in ten rivers of > this basin. Then, the "pollution level" are the treatment (with ten levels) > but if there is not a clean river in the basin, I cannot use a control ! > > Is this an experiment anyway ? > > Thanks for any comments..... > Voltolini > > _____________________________________________ > > Prof. J. C. VOLTOLINI > Grupo de Estudos em Ecologia de Mamiferos - ECOMAM > Universidade de Taubate (UNITAU) > Departamento de Biologia > Taubate, SP, Brasil. CEP 12030-010 > Tel: 0XX12-2254165 (lab.), 2254277 (secret. depto.) > FAX: 12 - 2322947 > E-Mail: [EMAIL PROTECTED] > _____________________________________________ > > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at > http://jse.stat.ncsu.edu/ > ================================================================= ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at http://jse.stat.ncsu.edu/ =================================================================
