Search results

  1. O

    Which test?

    When you run a regression, it also checks the model. Which IV is significant. It runs a t-test per each IV. The combination of the IV may have better results than checking separately the correlation of each IV with LOS But you also have multiple comparisons, so you need to adjust the...
  2. O

    Which test?

    Linear regression? Do you want to check how coat color, age, and breed predict the LOS?
  3. O

    Which test?

    What do you want to test?
  4. O

    What type of analysis? Ordinal Exposure, Dichotomous Outcome

    Hi Hehaoyue, Yes when the DV is categorical you should use the logistic regression (2 categories) or multinomial logistic regression (2 or more) I assume that the treatment to ordinal predictor in the logistic regression is similar to the treatment in the linear regression.
  5. O

    Comparing Medians

    Hi Hehaoyue, With sample size which is 30 or greater, you can run t-tests to compare the averages. As the averages distribute close to normal per CLT and t-test is less sensitive for the normality If you prefer to compare medians you may run the Mann-Whitney U test, this test compared the...
  6. O

    Tukey-like pairwise comparisons of variances

    I also don't like to use non-standard ways. I believe it should be okay, and I wrote the logic behind it. You may open a new question for another opinion. Levene's run the ANOVA over the differences, and Levene's test with two groups is equivalent to t-test over the differences. Tukey HSD is...
  7. O

    Tukey-like pairwise comparisons of variances

    Hi Zach, Probably not elegant: The following will do in R the Levene's test, and Tukey HSD for variances on the differences Using the ANOVA test instead of the Levene's test g1=c(1,2,2,3,3,4,4) g2=c(3,4,5,6,6,7,7,8,78) g3=c(3,4,4,4,5,34) len1=length(g1) len2=length(g2) len3=length(g3) data1...
  8. O

    Tukey-like pairwise comparisons of variances

    The Tukey table in the Levene's calculator compares the variances. nothing there is related to the comparison of the means. "it tells me that "differences" actually refers to group means" - It is the means of the differences ... confusing ...should be written differently! ...but when you run...
  9. O

    Tukey-like pairwise comparisons of variances

    Hi Katxt, It is not exactly the same test so I don't expect to get exactly the same result. You can see that most of the dots were near the origin, say a significant result as expected. I tried the same with a smaller difference between the SDs: SD1=2, SD2=2.2 (n=10 , rep=80) n=10 is a...
  10. O

    Tukey-like pairwise comparisons of variances

    Hi Katxt, How did you do the chart? What sample size did you use for each normal distribution? I used sample size=20 and got reasonable results (CLT) 50 repeats Even with sample size=10, It is still reasonable, 80 repeats ===================== #1: reps<-50 res1 <- numeric(reps) res2...
  11. O

    Long live SAS

    Before the commodore64 we had the Vic-20 with a tape :)
  12. O

    Tukey-like pairwise comparisons of variances

    So, can you agree to the following flow? 1. If Levene's test is a valid test for variances, we may use it to compare two sample variances. 2. The Levene's test over two samples is equivalent to two samples T-test over the differences (Pooled variance) 3. You may use two samples T-test over the...
  13. O

    Tukey-like pairwise comparisons of variances

    I assumes the Y-axis is the T p-value and X-axis is the F p-value?
  14. O

    error term in linear regression

    Hi S20, The residual is what the model can't predict, that's why it called residual...(I will not talk about the difference between residual and error) In your example, the model is Y=9+4X When x=1, predict Y=9+4*1=13, Y= 9+4*1+ (-3)
  15. O

    Tukey-like pairwise comparisons of variances

    Both tests, Levene's test and F test for two variances assumes normal population (of course when n>30 CLT works) Generally, with ANOVA test the normality assumption is not for each group but for the residuals. If each group distributes normally, then Normal - constant (average) also distribute...
  16. O

    Tukey-like pairwise comparisons of variances

    Yes, kind of, the Tukey HSD actually use the studentized range distribution Both F and T derives from the normal distribution. One way ANOVA - F right tail with 2 groups, equivalent to Two-sample t-test (pooled variance ) So if One way ANOVA on the differences - F right tail with 2 groups...
  17. O

    Tukey-like pairwise comparisons of variances

    Yes of course lockdown ... but can still jog outside :) Correct the absolute differences from the mean or from the median
  18. O

    Tukey-like pairwise comparisons of variances

    Hi Katxt, Lovely to chat with you :) I understand the same as you. I suggested running Tukey HSD on the differences frim the average of each group. Cheers
  19. O

    Tukey-like pairwise comparisons of variances

    If I understand you... you are not correct. 1. To compare the means you need to run the One way ANOVA test and then the "regular" Tukey HSD http://www.statskingdom.com/180Anova1way.html It will also give you the R code, so you may run on R if you don't trust an online calculator. 2. To compare...
  20. O

    Tukey-like pairwise comparisons of variances

    Hi Zach, Katxt When you compare the means you do the following: 1. Run One way ANOVA over the data 2. Run Tukey HSD To compare the variances you do the following: 1. Subtract the group's center from each value in each group (center = median or average) now you get processed data. 2. Run One...