Recent content by GretaGarbo

  1. GretaGarbo

    Best statistical method for CFU/ml?

    What is "CFU/ml"?
  2. GretaGarbo

    Caclulating Sample Size

    Look at this wikipedia page about the power of test at the example section. With sigma/sqrt(n) you can replace that with (sigma/sqrt(n))*sqrt((N-n)/(N-1)) where N is the populations size. But if N is large (say larger than 1000) and n is small (say 50) then you are essentially dividing 1...
  3. GretaGarbo

    Is Multivariate Analysis possible?

    OK! Prove it! Or show a published paper that support that claim!
  4. GretaGarbo

    Is Multivariate Analysis possible?

    I agree with most of what J58 has said. But not with this statement. I believe that it come from one publication where in that application it happened that the sample size was 10 times the number of explanatory variables. In reality they have no relation. Compare the Placket Burman design where...
  5. GretaGarbo

    Number of measurements

    Hmm, usually the sample size is equal to the number or measurements. What do you (altf2) mean by this? Also, one way a sample can be "representative" is when every individual has the same chance of being included, like in simple random sampling.
  6. GretaGarbo

    Reaction times analysis with Mixed Models

    I would guess that reaction times would be a skewed distribution. So maybe a gamma distribution fits. Or maybe a lognormal distribution. Maybe they don't have that on the standard software. Then try to take the logarithm (so that data transforms from the lognormal to the normal distribution).
  7. GretaGarbo

    Box Cox Power Transformation versus Blom Transformation -IQ

    I also have a question: What happened to you? Why ask a question and then not return? Events like this makes me more reluctant to answer in the future.
  8. GretaGarbo

    Box Cox Power Transformation versus Blom Transformation -IQ

    What is "blom transformation"? (Or do you mean Gunnar Blom's transformation to a QQ-plot?) Why don't you show us your data and code?
  9. GretaGarbo

    R Studio: Numerical Example where qnorm() and pnorm() are not exact inverses?

    x <- 1:15 p <- pnorm(x, mean = 5, sd=2) p x2 <- qnorm(p, mean = 5, sd=2 ) x2 x- x2 [1] 0.000000e+00 -4.440892e-16 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 [8] 0.000000e+00 0.000000e+00 3.552714e-15 7.105427e-15 3.375078e-14 0.000000e+00 1.083578e-12 [15]...
  10. GretaGarbo

    Starting Values for a non-linear regression

    Look att Wikipedia on the Weibull distribution and write the equation like in the Weibull plot section. You can do the maximum likelihood estimation and use a starting value of say k=3.
  11. GretaGarbo

    What statistical model to be used?

    What design were you thinking of here?
  12. GretaGarbo

    Permutation test with skewed data

    Since the data are continuous data originally, that have been rounded, you could think of the zero value as a censored value. If the original data was between 0 and 0.5, but then it has been rounded to 0, you can think of it as censored below 0.5. If you have two values y1 and y2, you can...
  13. GretaGarbo

    A quesion about Percentile

    The simplest thing would be to do linear interpolation. LMS stand for Lambda, mu and sigma and was sugested by Cole(1988) and Cole & Green (1992). Now gamlss is the WHO standard ( look at their home page). The distribution is (in general not) normally distributed. Suggested distributions are...
  14. GretaGarbo

    Which stats test to use?

    How about histograms and boxplots for "line was not running" and "line was running" and then do a t-test on the response variable. Does the data look normally distributed?
  15. GretaGarbo

    What statistical model to be used?

    I would suggest that you combine your bacteria. It is more interesting to see the combined effekt of two or three bacteria. Let your bacteria be f= florida, e= eryngii, o=osteatus. 0 is without the bacteria and 1 is with the bacteria. Like this: f e o 0 0 0 1 0 0 0 1 0 1 1 0 0 0 1 1 0 1 0 1 1...