osiander@24on.cc
2002-Apr-15 21:20 UTC
[R] simple Q: required sample size & usage of power.t.test()
Hi community, Seems I am too stupid: I try to calculate with power.t.test() an example from the statistics textbook [Jerrold H. Zar, Biostatistical Analysis, 2nd edition, Prentice Hall, 1984, Chapter 8, Exercise 8.4, (page 120)]: ------- A sample of size 18 has a mean of 13.55cm and a variance of 6.4512cm^2. (a) Calculate the 95% confidence interval for the population mean. (b) How large a sample would have to be taken from this population to estimate ยต to within 1.00cm, with 95% confidence? (c) 2.00cm with 95% confidence? (d) 2.00cm with 99% confidence? Result should be - according to the answers appendix - (a) 13.55 +- 1.26cm (b) n=29, (c) n=10, (d) n=11 ------- Here my questions: (1) which functions in R can be used to solve (a) (2) what has to be the syntax to answer (b), (c) and (d) ? Thanks in advance, Osiander -- osiander at 24on.cc -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Peter Dalgaard BSA
2002-Apr-15 21:50 UTC
[R] simple Q: required sample size & usage of power.t.test()
osiander at 24on.cc writes:> Hi community, > > Seems I am too stupid: > > I try to calculate with power.t.test() an example from the statistics textbook [Jerrold H. Zar, Biostatistical Analysis, 2nd edition, Prentice Hall, 1984, Chapter 8, Exercise 8.4, (page 120)]:Ah, this is not a standard sample size calculation, but a pedagogical exercise. t tests and power.t.test are irrelevant for this.> ------- > A sample of size 18 has a mean of 13.55cm and a variance of 6.4512cm^2. > (a) Calculate the 95% confidence interval for the population mean. > (b) How large a sample would have to be taken from this population to estimate ? to within 1.00cm, > with 95% confidence? > (c) 2.00cm with 95% confidence? > (d) 2.00cm with 99% confidence? > > Result should be - according to the answers appendix - (a) 13.55 +- 1.26cm (b) n=29, (c) n=10, (d) n=11 > ------- > > Here my questions: > > (1) which functions in R can be used to solve (a) > (2) what has to be the syntax to answer (b), (c) and (d) ?Hmmm, now are you trying to learn R for yourself by trying it on some textbook examples, or are you trying to get us to help with your homework? Either way: You'll need the formula for the confidence interval (presumably a couple of pages earlier in the book). The qnorm() function gives you quantiles of the Normal distibution, the rest should be basic algebra. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._