For this case I would use a permutation test. Start by choosing some statistic that represents your 4 students across the different grades, some possibilities would be the sum of scores across grades and students, or mean, or median, or ...
Compute the selected statistic for your 4 students and save that value. Now select 4 students at random and compute the same statistic, repeat this a bunch of times (thousands) and compute the statistic each time. All those stats on the random selections represent the distribution of the statistic under the null hypothesis that your 4 students were randomly chosen (vs. chosen based on something that is related to the grade). Now you just compare the stat on the original 4 students to the distribution (if you need a specific p-value it is just the proportion of the random stats that are as or more extreme as your original 4). On Sat, Mar 10, 2012 at 4:04 AM, aoife doherty <aaral.si...@gmail.com> wrote: > Thank you for the replies. > So what my test wants to do is this: > > I have a big matrix, 30 rows (students in a class) X 50 columns (students > grades for the year). > An example of the matrix is as such: > > > grade1 grade2 grade3 ..... grade 50 > student 1 > student 2*** > student 3 > student 4*** > student 5*** > student 6 > . > . > . > . > . > student 30*** > > As you can see, four students (students 2,4,5 and 30) have stars beside > their name. I have chosen these students based on a particular > characteristic that they all share.I then pulled these students out to make > a new table: > > grade1 grade2 grade3 ....... grade 50 > > student 2 > student 4 > student 5 > student 30 > > > and what i want to see is basically is there any difference between the > grades this particular set of students(i.e. student 2,4,5 and 30) got, and > the class as a whole? > > So my null hypothesis is that there is no difference between this set of > students grades, and what you would expect from the class as a whole. > > Aaral > > > > > > > On Sat, Mar 10, 2012 at 12:18 AM, Greg Snow <538...@gmail.com> wrote: >> >> Just what null hypothesis are you trying to test or what question are >> you trying to answer by comparing 2 matrices of different size? >> >> I think you need to figure out what your real question is before >> worrying about which test might work on it. >> >> Trying to get your data to fit a given test rather than finding the >> appropriate test or other procedure to answer your question is like >> buying a new suit then having plastic surgery to make you fit the suit >> rather than having the tailor modify the suit to fit you. >> >> If you can give us more information about what your question is we >> have a better chance of actually helping you. >> >> On Fri, Mar 9, 2012 at 9:46 AM, aoife doherty <aaral.si...@gmail.com> >> wrote: >> > >> > Thank you. Can the chi-squared test compare two matrices that are not >> > the >> > same size, eg if matrix 1 is a 2 X 4 table, and matrix 2 is a 3 X 5 >> > matrix? >> > >> > >> > >> > On Fri, Mar 9, 2012 at 4:37 PM, Greg Snow <538...@gmail.com> wrote: >> >> >> >> The chi-squared test is one option (and seems reasonable to me if it >> >> the the proportions/patterns that you want to test). One way to do >> >> the test is to combine your 2 matrices into a 3 dimensional array (the >> >> abind package may help here) and test using the loglin function. >> >> >> >> On Thu, Mar 8, 2012 at 5:46 AM, aaral singh <aaral.si...@gmail.com> >> >> wrote: >> >> > Hi.Please help if someone can. >> >> > >> >> > Problem: >> >> > I have 2 matrices >> >> > >> >> > Eg >> >> > >> >> > matrix 1: >> >> > Freq None Some >> >> > Heavy 3 2 5 >> >> > Never 8 13 8 >> >> > Occas 1 4 4 >> >> > Regul 9 5 7 >> >> > >> >> > matrix 2: >> >> > Freq None Some >> >> > Heavy 7 1 3 >> >> > Never 87 18 84 >> >> > Occas 12 3 4 >> >> > Regul 9 1 7 >> >> > >> >> > >> >> > I want to see if matrix 1 is significantly different from matrix 2. I >> >> > consider using a chi-squared test. Is this appropriate? >> >> > Could anyone advise? >> >> > Many thank you. >> >> > Aaral Singh >> >> > >> >> > -- >> >> > View this message in context: >> >> > >> >> > http://r.789695.n4.nabble.com/help-please-2-tables-which-test-tp4456312p4456312.html >> >> > Sent from the R help mailing list archive at Nabble.com. >> >> > >> >> > ______________________________________________ >> >> > R-help@r-project.org 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. >> >> >> >> >> >> >> >> -- >> >> Gregory (Greg) L. Snow Ph.D. >> >> 538...@gmail.com >> >> >> >> ______________________________________________ >> >> R-help@r-project.org 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. >> > >> > >> >> >> >> -- >> Gregory (Greg) L. Snow Ph.D. >> 538...@gmail.com >> >> ______________________________________________ >> R-help@r-project.org 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. > > -- Gregory (Greg) L. Snow Ph.D. 538...@gmail.com ______________________________________________ R-help@r-project.org 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.