Example 67.1 One-Way ANOVA
This example deals with the same situation as in Example 41.1 of Chapter 41, The GLMPOWER Procedure.
.64-Bit versions of JMP and JMP Pro only.JMP is an in-memory analysis tool. Your memory requirements will depend on the amount of data being analyzed. JMP does not support the FileMaker Pro database on Windows.
Hocking (1985, p. 109) describes a study of the effectiveness of electrolytes in reducing lactic acid buildup for long-distance runners. You are planning a similar study in which you will allocate five different fluids to runners on a 10-mile course and measure lactic acid buildup immediately after the run. The fluids consist of water and two commercial electrolyte drinks, EZDure and LactoZap, each prepared at two concentrations, low (EZD1 and LZ1) and high (EZD2 and LZ2).
You conjecture that the standard deviation of lactic acid measurements given any particular fluid is about 3.75, and that the expected lactic acid values will correspond roughly to those in Table 67.31. You are least familiar with the LZ1 drink and hence decide to consider a range of reasonable values for that mean.
Water | EZD1 | EZD2 | LZ1 | LZ2 |
35.6 | 33.7 | 30.2 | 29 or 28 | 25.9 |
You are interested in four different comparisons, shown in Table 67.32 with appropriate contrast coefficients.
Contrast Coefficients | |||||
|---|---|---|---|---|---|
Comparison | Water | EZD1 | EZD2 | LZ1 | LZ2 |
Water versus electrolytes | 4 | –1 | –1 | –1 | –1 |
EZD versus LZ | 0 | 1 | 1 | –1 | –1 |
EZD1 versus EZD2 | 0 | 1 | –1 | 0 | 0 |
LZ1 versus LZ2 | 0 | 0 | 0 | 1 | –1 |
For each of these contrasts you want to determine the sample size required to achieve a power of 0.9 for detecting an effect with magnitude in accord with Table 67.31. You are not yet attempting to choose a single sample size for the study, but rather checking the range of sample sizes needed for individual contrasts. You plan to test each contrast at . In the interests of reducing costs, you will provide twice as many runners with water as with any of the electrolytes; in other words, you will use a sample size weighting scheme of 2:1:1:1:1. Use the ONEWAYANOVA statement in the POWER procedure to compute the sample sizes.
Jmp Pro 12.1.0 2016
The statements required to perform this analysis are as follows:
Jmp Pro 12.1.0 Mac
The NTOTAL= option with a missing value (.) indicates total sample size as the result parameter. The GROUPMEANS= option with values from Table 67.31 specifies your conjectures for the means. With only one mean varying (the LZ1 mean), the 'crossed' notation is simpler, showing scenarios for each group mean, separated by vertical bars (|). See the section Specifying Value Lists in Analysis Statements for more details on crossed and matched notations for grouped values. The contrasts in Table 67.32 are specified with the CONTRAST= option, by using the 'matched' notation with each contrast enclosed in parentheses. The STDDEV=, ALPHA=, and POWER= options specify the error standard deviation, significance level, and power. The GROUPWEIGHTS= option specifies the weighting schemes. Default values for the NULLCONTRAST= and SIDES= options specify a two-sided test of the contrast equal to 0. See Output 67.1.1 for the results.
Jmp Pro 12.1.0 Download
| Fixed Scenario Elements | |
|---|---|
| Method | Exact |
| Alpha | 0.025 |
| Standard Deviation | 3.75 |
| Group Weights | 2 1 1 1 1 |
| Nominal Power | 0.9 |
| Number of Sides | 2 |
| Null Contrast Value | 0 |