Presentation on theme: "Statistical Techniques I EXST7005 Miscellaneous ANOVA Topics & Summary."— Presentation transcript:
Statistical Techniques I EXST7005 Miscellaneous ANOVA Topics & Summary
LSMeans calculation n The calculations of LSMeans is different. For a balanced design, the results will be the same. However, for unbalanced designs the results will often differ. n The MEANS statement in SAS calculates a simple mean of all available observations in the treatment cells. n The LSMeans statement will calculate the mean of the treatment cell means.
LSMeans calculation (continued) n Example: n The MEAN of 4 treatments, where the observations are 3,4,8 for a1, 3,5,6,7,9 for a2, 7,8,6,7 for a3 and 3,5,7 for a4 is n The individual cells means are 5, 6, 7 and 5 for a1, a2, a3 and a4 respectively. The mean of these 4 values is This would be the LSMean.
Treatments a1a2a3Means b b Means Raw means
Treatments a1a2a3Means b b Means LSMeans means Treatments a1a2a3Means b1 6.5 b2 6.6 Means
Confidence Intervals on Treatments Like all confidence intervals on normally distributed estimates, this will employ a t value and will be of the form Mean ta/2(S Y) n The treatment mean can be obtained from a means (or LSMeans) statement, but the standard deviation provided is not the correct standard error for the interval.
Confidence Intervals on Treatments (continued) n The standard error is the square root of MSE/n, where n is the number of observations used in calculating the mean. n The degrees of freedom for the tabular t value is the d.f. from the MSE used to calculate the standard error.
Confidence Intervals on Treatments (continued) n If there are several error terms (e.g. experimental error and sampling error) use the one that is appropriate for testing the treatments.
Exam Coverage n ANOVA (one-way and two-way) will be covered. n Be aware of similarities and differences with the t-test. n HOV tests and tests of normality will be included n Factorial treatment arrangement (two-way) with interpretation interactions will be covered
Exam Coverage (continued) n RBD will be covered only as the concepts. How is the linear model different, why do we block, what is a block, etc. No SAS output on RBD. n Be able to interpret and discuss Post-ANOVA tests è contrasts è range tests
Exam Coverage (continued) n Be able to place a confidence interval on a treatment mean. n Recognize designs and treatment arrangements from a described problem. è be able to determine the experimental unit, sampling unit, and get the d.f. error. n Answers to questions will be on the net. n Good Luck.