105StorageTimeExample(1)

105StorageTimeExample(1) - EXAMPLE ANALYSIS OF AN...

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EXAMPLE ANALYSIS OF AN UNBALANCED TWO-FACTOR EXPERIMENT An experiment was conducted to study the effect of storage time and storage temperature on the amount of active ingredient present in a drug at the end of storage. Sixteen vials of the drug, each containing approximately 30 mg/mL of active ingredient, were assigned (using a completely randomized design) to the following treatments: 1. Storage for 3 months at 20 C 2. Storage for 3 months at 30 C 3. Storage for 6 months at 20 C 4. Storage for 6 months at 30 C Six of the 16 vials were damaged during shipment to the laboratory where the active ingredient was measured. Accurate measures of the amount of active ingredient could be obtained only for the 10 undamaged vials. The table below shows the amount of active ingredient lost during storage (in tenths of mg/mL) for each of the undamaged vials. Copyright c ± 2011 Dept. of Statistics (Iowa State University) Statistics 511 1 / 1
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Storage Temperature Storage Time 20 C 30 C 3 months 2 5 9 12 15 6 months 6 6 7 7 16 We call an experiment balanced if all treatments have the same number of experimental units. Although this experiment was designed to be balanced with 4 experimental units per treatment, it has become unbalanced because the number of measured experimental units varies with treatment. Copyright c ± 2011 Dept. of Statistics (Iowa State University) Statistics 511 2 / 1
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Our discussion focuses on 2 way factorials, issues same for > 2 way I When design is balanced, lots of nice things happen simple analysis I When unbalanced, need to either: I think carefully about what you’re doing I or, know what happens by default. Make sure you’re getting what you really want. I The following should be a review of 500/402. If not, get help in office hours. I Our approach to unbalanced ANOVA is the generally accepted approach in the US. Sometimes called “the SAS approach”. Not universal. UK users, especially John Nelder differ. Nelder had a huge influence on R. I
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This note was uploaded on 02/11/2012 for the course STAT 511 taught by Professor Staff during the Spring '08 term at Iowa State.

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105StorageTimeExample(1) - EXAMPLE ANALYSIS OF AN...

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