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mathews ● 2008-01-08 08:47 (6330 d 14:33 ago) Posting: # 1475 Views: 14,721 |
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Hai All,  Anybody please tell me what is the advantage of using Proc MIXED insted of Proc GLM in the SAS program, for the analysis of bioequivalence studies with missing values (subjects not completed some periods). Is it required to specify in the protocol that which procedure (GLM or MIXED) is use for the statistical analysis. regards, Matz. |
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H_Rotter ★ Germany, 2008-01-08 14:20 (6330 d 09:00 ago) @ mathews Posting: # 1480 Views: 12,706 |
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Hi Matz! ❝ Hai All ^^ -- that's German for 'shark'  ❝ Anybody please tell me what is the advantage of using Proc MIXED insted of Proc GLM in the SAS program, for the analysis of bioequivalence studies with missing values (subjects not completed some periods). See this post by Jaime and Helmut's as well. So if you have more than two treatments in your study you may use Proc MIXED. In a 2×2 study you will get the same results - but Proc MIXED is more time consuming (iterative instead of explicit). ❝ Is it required to specify in the protocol that which procedure (GLM or MIXED) is use for the statistical analysis. IMHO that's a good idea. Simply specify it as a decision tree: No drop-outs (complete data from all periods) → Proc GLM Drop-outs (incomplete data) → Proc MIXED Regards, Hermann |
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mathews ● 2008-01-17 09:02 (6321 d 14:17 ago) @ H_Rotter Posting: # 1518 Views: 12,371 |
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Thanks Mr Herman One more doubt. I used both MIXED and GLM procedure to analyse the data of a 2x2 design with missing values. But both procedure gave me the same result (i.e; 90%C.I and ANOVA table). So what is the advantage of using MIXED procedure for missing data set?....Is there any particular reason for using MIXED procedure for analysing missing data sets? regards matz |
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H_Rotter ★ Germany, 2008-01-18 00:29 (6320 d 22:51 ago) @ mathews Posting: # 1522 Views: 12,507 |
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Dear matz! ❝ I used both MIXED and GLM procedure to analyse the data of a 2x2 design with missing values. But both procedure gave me the same result (i.e; 90%C.I and ANOVA table). As my subject line already said: 'Proc Miced for >2treatments' In a 2x2 study there is no information which can be 'recovered' by using Proc MIXED - you simply have no test/reference ratio for drop-outs (incomplete samples). Therefore these subjects are omitted in both methods - giving identical results. ❝ So what is the advantage of using MIXED procedure for missing data set? ....Is there any particular reason for using MIXED procedure for analysing missing data sets? Only for more than 2 treatments. Please reread my previous post and the linked ones as well...  Regards, Hermann |
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mathews ● 2008-01-18 13:56 (6320 d 09:24 ago) @ H_Rotter Posting: # 1525 Views: 12,458 |
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Dear Hermann! thank u so much for your reply... One more clarrification please....U said Proc Mixed is for >2treatments but FDA guideline "Statistical Approaches to Establishing Bioequivalence" says PROC MIXED in SAS should be used for the analysis of replicated crossover studies for average BE[p.13]. Is there any particular reason behind this?  .Because 2 treatment 4 period design is a replicate crossover design. I compare a sample data set of 2x4 design with missing values (example 4.4 in the text "BIOEQUIVALENCE and STATISTICS in CLINICAL PHARMACOLOGY") using both GLM and MIXED procedure. both will give same output. then why FDA says to use MIXED procedure for replicate crossover design?. Any reason?..... someone says GLM procedure deletes the entire subject from an analysis if that person has any missing data,but MIXED does not. Is it correct? Regards Matz |
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H_Rotter ★ Germany, 2008-01-18 14:25 (6320 d 08:55 ago) @ mathews Posting: # 1526 Views: 12,686 |
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Dear Matz! ❝ thank u so much for your reply... Welcome! ❝ One more clarrification please....U said Proc Mixed is for >2treatments but FDA guideline "Statistical Approaches to Establishing Bioequivalence" says PROC MIXED in SAS should be used for the analysis of replicated crossover studies for average BE[p.13]. ❝ Is there any particular reason behind this? Example of a [TRTR – RTRT] replicate design: If a subject in the second sequence drops out in the last period you have data from three periods; two values of the reference (from periods I & III), and one value of the test (from period II). Proc GLM drops the entire subject, but Proc Mixed uses all available data. ❝ Because 2 treatment 4 period design is a replicate crossover design. I compare a sample data set of 2x4 design with missing values (example 4.4 in the text "BIOEQUIVALENCE and STATISTICS in CLINICAL PHARMACOLOGY") using both GLM and MIXED procedure. both will give same output. then why FDA says to use MIXED procedure for replicate crossover design?. ❝ Any reason?..... OK, you are right - my answer was not correct (I had some type of Williams' design in mind). It should read 'Proc Mixed for >2 periods'. ❝ someone says GLM procedure deletes the entire subject from an analysis if that person has any missing data, but MIXED does not. Is it correct? Yes, this is correct (see above). Sorry for my confusing previous answer. Regards, Hermann |
Ing. Helmut Schütz