At 05:55 03/12/2006, Ethan Johnsons wrote: >I have the clinical study data. > > Year 0 Year 3 >Retinol (nmol/L) N Mean +-sd Mean +-sd >Vitamin A group 73 1.89+-0.36 2.06+-0.53 >Trace group 57 1.83+-0.31 1.78+-0.30 > >where N is the number of male for the clinical study. > >I want to test if the mean serum retinol has increased over 3 years >among subjects in the vitamin A group.
If you want to test means why did you think a test for proportions was a good idea? >> 1.89+0.36 >[1] 2.25 >>1.89-0.36 >[1] 1.53 >>2.06+0.53 >[1] 2.59 >>2.06-0.53 >[1] 1.53 > > >>prop.trend.test(c(2.25, 1.53),c( 2.59, 1.53)) > > Chi-squared Test for Trend in Proportions > >data: c(2.25, 1.53) out of c(2.59, 1.53) , >using scores: 1 2 >X-squared = 0.2189, df = 1, p-value = 0.6399 > >The issue I am seeing that N of Vitamin A group = 73 seems not reflected. >This leads me to think that I can't implement the test based on the >data just presented. >Nor a two-tailed test is possible. > > 2-sample test for equality of proportions with continuity correction > >data: c(2.25, 1.53) out of c(2.59, 1.53) >X-squared = 0, df = 1, p-value = 1 >alternative hypothesis: two.sided >95 percent confidence interval: >-0.6738203 0.4112720 >sample estimates: > prop 1 prop 2 >0.8687259 1.0000000 > >Warning message: >Chi-squared approximation may be incorrect in: prop.test(c(2.25, >1.53), c(2.59, 1.53)) > >Any ideas, please? > >thx > >ej > > Michael Dewey http://www.aghmed.fsnet.co.uk ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
