# covariance

1. ### xtmixed covariances: why it doesn't work??

Hi, I'm trying for weeks to run the following model: mi estimate, variance : xtmixed MathG5 MathG4 , || classID:, covariance(unstructured) || studentID: , covariance(unstructured) This is only the first model, I want to add a lot more covariates and interaction effects, but if the first...
2. ### Covariance of two functions for error propagation

Hi all, I have two functions: X=A-B Y=A+2B I need to calculate the covariance of X and Y in terms of the (known) variances of A and B as part of a propagation of uncertainty calculation to work out the error on a derived quantity Z=X/Y. All I can find information on is how to...
3. ### High covariance between two factors. Is that a problem in a regression?

Hi, Is it problematic if there is a very high covariance between two factors (independent latent variables) (0.95 standardized). I thought the implication of two independent variables that covary to a high degree was that they are likely to have almost the same effect on a specific...
4. ### Covariance and Correlation for Regression Model

I've been looking over some regression models lately and I came across one which, although similar, differs from the "standard" simple linear model. I was hoping somebody could provide some assistance with some properties that I'm confused with. Assuming the regression form: y_{i} = \beta_{0}...
5. ### Covary out?

Hi all! Thanks in advance for the help! I have three variables A, B, and C A is an independent, two category variable B is an independent, continuous variable C is a dependent, continuous variable. I want to check if there is a relationship between A and C (i.e., are there...
6. ### Covariance of random balls

Hi, would appreciate any comments: I have: 10 balls with number 6 on each, 10 balls with n. 7, 10 balls with n. 8. So it's 30 balls in total and now I take 10 balls at random (X1, ..., X10), without replacement. The question is cov(X1, X2) = ? (covariance of the first and second ball) I...
7. ### Covariance

I have a problem with a contingency table for X=1, 2, 3 and Y = 1 and 2. In a related question, the correlation is asked for X and Y. As far as I know, the correlation needs the covariance in the nominator. Unfortunately, i am unable to apply the formulae for the covariance. How did you...
8. ### AMOS SEM model drawing rules

hi! This is my first attempt to draw a model in SPSS AMOS 19. I am confused by seeing that I cannot draw covariance arrow between two variables, A and B provided there is a path arrow pointing from C to one of them. Could you explain it to me? What is the difference between drawing two...
9. ### Mixed Model Covariance Structure

I have a study with a somewhat unique experimental design which I would like to used Mixed Modeling to analyze. All subjects in the study were tested at baseline. Three repeated measurements (dependent variable) were collected on them under controlled conditions (ie, Pre-Exposure, During...