1. victorxstc

    Do TSers pick threads with titles indicating misery or urgent help?

    Following our previous talk, I wanted to compare two TS members right now. I counted how many threads of two TSers had titles like "Please help", "Help", "lost", "Urgent" etc. One of TSers had responded to 25 threads out of about 200 threads they had answered to. The other one had picked almost...
  2. J

    non-central chi-square distribution.

    If X_i is distributed as normal with mean \mu and variance-covariance matrix D,where D is the diagonal matrix, then show that X^TD^{-1}D is distributed as noncentral \chi^2 with k degrees of freedom and noncentrality parameter \mu^TD^{-1}\mu=\lambda.
  3. J

    What will be the transformation and Jacobian of transformation for the following case

    Let X_i\sim N(\mu_i,\sigma^2) ; where [i=1,2,\ldots,n] show that \bar X and (X_i-\bar X) are independent. If all X_i had same mean \mu then we transform the random variables X_i; [i=1,2,\ldots,n] to Y_1=\bar X Y_2 =X_2-\bar X Y_3 = X_3-\bar X \vdots Y_n = X_n-\bar X...
  4. S

    Non-parametric Chi-square test outputs *different* when order is reversed?

    Hello, I am a physics graduate student and am conducting research on physics learning and teaching. I surveyed n=63 students Likert scale 1 to 4 pre and post month-long intervention to determine whether treatment works. The following has put me into a wall. Question: Does it make a...
  5. P

    Interpretation of Monte Carlo Significance for Chi-Square Analysis

    I am currently utilizing a 4x7 chi-square and cannot collapse any columns or rows, resulting in expected cell counts of less than 5 in 14 cells (50%), minimum expected value is 1.36. I included a monte carlo test of significance to account for this, however, I am unclear on how to interpret...
  6. K

    Alternatives to logistic regression when the number of cases is low

    Hi All I got involved in my first foray into logistic regression, but have come to realize that I probably can't use it. Let me tell you about my data. I am investigating the consumption of 3 different insect pests by bats in an agricultural area. The response variable is binary for each...
  7. S

    Using the F distribution to find a probability

    Ok so here is my question and the steps I have taken: Question: If X and Y are independent random variables having chi-square distributions with 12 and 6 degrees of freedom respectively, find P(X > 8Y). So here is what I have done: F = (X/v1)/(Y/v2) P(X > 8Y) = P(X/Y > 8) = P(F >...
  8. S

    Use Normal Distribution and Chi-square distribution

    My question is as follows: If X and Y are independent random variables, X has a normal distribution with mean 2 and variance 4, and Y has a chi-square distribution with 9 degrees of freedom, then find "u" such that: P(X > 2 + u√(y) = .01 note: "√" stands for square root Anyway, I...
  9. T

    T-Test with Chi-Square

    Is the t-test always used with chi-square?
  10. E

    Chi-Square GOF test results appear to change with size of sample

    Hi, I have not been able to find anything related to this topic on the web or on this site. I am not even sure what words to use in the search. So, please help me understand what is going on so that I know if I am using this test correctly. In experimenting with the Chi-Square Goodness of Fit...
  11. T


  12. K

    HELP!!! Chi-Square Tests

    What is the difference between Homogeneity of proportions across two or more groups, Test of independence, and Goodness of fit test? Also, how would you know which test was used if all you are given is X-squared=31.3695, df=2, p-value=1.542e-07? And based on those outputs, how do you...
  13. F

    Difference of 2 Chi-Square Variables Still a Chi-Square Variable?

    I did a problem for homework that made me show that the sum of two chi-square variables is still a chi-square variable. However, when I find the difference, the book says it is no longer a chi-square variable if the degrees of freedom in the exponent of the MGF is positive. The MGF still has...
  14. O

    Turing test analysis

    Hi, I’m having problems with the analysis of one of the tests I’ve done on the evaluation of synthetic speech. The test was set-up like a Turing-Test: to each test subject, 20 sentences were shown (10 original and 10 synthetic). The subjects had to guess for each sentence if it was original...
  15. C

    Can I use a chi-square test for this 2x3 contingency table?

    Imagine I want to find out whether there are any differences between male and female participants in their pet choices, and this is my 2x3 contingency table: ___________ Dog_____Cat_____Bird Male_______ 75_____ 51_____ 27 Female _____60 _____ 80 _____ 9 Note I don't have the same amount...
  16. S

    How to analyze if there is a difference between grades?

    Hi, Could you please help me which stata command I should use to see if there is a difference in improvements by grade level? I am thinking chi-square, but not 100% sure. Thank you for your help! 6th Grade 7th Grade 8th Grade Frequency Percent Frequency Percent...
  17. C

    single-case study

    Dear friends, I am running a single case study. I am collecting correct and incorrect responses on two similar tests in 3 moments in time. I would like to know two things: - if there exist significant differences between each of the three times within each test and where are those...
  18. U

    Chi-Square Question

    I want to see if one population of trees has a significantly lower density of seedlings than two other populations of trees becasue it certainly appears to that way. So I set up the chi-square test like this: # Seedlings # Hectares Population 1 35...
  19. U

    Chi-square test

    I am trying to use chi-square in an ecological application to compare the densities of trees per hectare over 3 different populations? (such as 35 seedlings in a 12 hectare area vs 250 seedlings in a 16 hectare area vs 332 seedlings in a 24 hectare area). is this an appropriate use of the...
  20. P

    deriving chi-square stat for contingency table

    Howdy! I'm attempting to derive the chi-square stat for a 2x2 contingency table, like: a | b ------ c | d The chi-square formula given is : (a+b+c+d)(ad- bc)^2 / ( (a+b)(a+c)(b+d)(c+d) ) I can derive all but the (ad-bc)^2 part of the formula. Any links or tips about how this formula...