EXST7015 Fall2011 Design Id

EXST7015 Fall2011 Design Id - EXST7015 : Statistical...

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EXST7015 : Statistical Techniques II Geaghan ANOVA Design Identification Page 5 James P. Geaghan - Copyright 2011 Experimental Design Identification To correctly design an experiment, or to analyze a designed experiment, you must be able to look at a design situation and correctly assess the salient aspects of the design. I will ask you to identify the design, the treatment variable, dependent variable, degrees of freedom error, experimental unit, sampling unit (if any), and if the treatment is fixed or random. To begin with, determine what the investigators are trying to do and what they plan to measure. What is the Objective of the study? Specifically, what hypotheses are to be tested? What is the variable of interest? What unit is the treatment applied to? What, exactly, is the unit measured? Suppose an investigator wants to compare the oxygen levels in seven predefined "habitats" in the Louisiana marsh. He will randomly select and sample 4 sites in each habitat. One oxygen measurement is made at each site. What variable is being measured? This variable will produce a series of measurements or quantities? Oxygen levels (usually in ppm) What are the treatments ? What is the investigator interested in comparing or testing for differences? Habitats (t=7) Are there any blocks (i.e. sources of variation that should be recognized, but which are not important to the investigator). For example, did he replicate the experiment in several different rivers or several locations along the coast? Are the 4 “replicates” just multiple observations or are they taken in 4 separate places? Apparently no blocks. What are the experimental units for the experiment? What unit was the treatment applied to or what was sampled for each treatment (habitat)? A site (s=4) Are there separate sampling units at each site, or is only one measurement taken in each experimental unit? In this case it is a water sample on which oxygen is measured. Since there is only a single sample at each site we can consider each sample to represent the site. Also the sites If there were multiple samples taken at each site these would be the sampling units. These in turn can be split into sub-sampling units. Apparently this was not done. Is that all? There are other issues, not all of which we have covered. Are the treatments fixed or random? Is the design balanced? Are there any particular hypothesis tests of interest (contrasts)? Are the treatment levels quantitative? Any other special post ANOVA applications? The topic of “Design” will be discussed in the second half of the course. For the moment our objective is only to learn to identify the components of an experiment. Therefore, I will put a design description on the Internet and during each class period I expect you to have looked at it and to be prepared to answer the following questions.
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EXST7015 : Statistical Techniques II Geaghan ANOVA Design Identification Page 6 James P. Geaghan - Copyright 2011 Questions: 1) What is the treatment arrangement for this experiment?
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This note was uploaded on 12/29/2011 for the course EXST 7015 taught by Professor Wang,j during the Fall '08 term at LSU.

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EXST7015 Fall2011 Design Id - EXST7015 : Statistical...

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