1. S

    Need help with medical study

    Hi, I'm writing a medical paper on asthma and I'm afraid I 've reached a point where I am unconfident of my statistics knowledge. I am hypothesizing that there is a relationship between elevated concentrations of a substance in the blood (we will call it X) and severity of asthma...
  2. R

    Can a relative risk and odds ratio differ in p-value?

    With increasing incidence of the outcome, odds ratios tend to overestimate relative risks. I was wondering whether they also start to differ in p-values. So my question is: could there be a situation where the (unadjusted) odds-ratio reaches statistical significance, but the (unadjusted)...
  3. R

    How to calculate p-value of two-sample t-test

    I have 2 independent data sets, and I know the following about each of them: mean, SD, and sample size. I calculated the t-statistic just fine my.t.test<-function(mu1, mu2, sd1, sd2, n1,n2){ t=(mu1-mu2)/sqrt((sd1)^2/n1+(sd2)^2/n2) return(t) } I know that the degrees of freedom...
  4. K

    p-value in a two-tailed hypothesis test

    how do i find the p-value of a two-tailed hypothesis test based on a large sample if I have a test staistic eqaul to 0.95
  5. S

    Model selection for logistic regression, comparing p-value approach, BIC and CV.

    Hi, I need to write a discussion on three approaches of model selection; p-value, Bayes factors (using BIC) and leave-one-out cross validation. The p-value is not preferred, statiscal significance depends on sample size, p-value is based on imaginary data, depends on the intentions of the...
  6. S

    p-value associated with Kruskal Wallis with multiple comparison?

    I have a data set that shows the differences between 3 different controllers of a biomechanical system on the same performance metric (specifically, I measure each controller's performance on a set of N tasks, and record the percentage of tasks that achieve success (i.e. the controlled segment...
  7. S

    calculating p-value from resampling of the null distribution

    Hi all, i am a PhD student in Bioinformatics and i'm dealing with some statistics issue in my reasearch; i was hoping you could lend me a hand :D I am dealing with a pool of datapoints (let's call it Q). I selected a subset of Q according to some particular characteristics, i will call...
  8. L

    Seeing a trend in my SPSS T-tests, is this normal?

    Hello all. While attempting to complete my homework for my Stats class on SPSS I noticed on 3 out of the 4 problems I've done so far, I have gotten .000 for the p-value. Two were Independent T-tests and the other was a One-sample T-test. Is there something that I'm missing or could be entering...
  9. L

    Removing interaction effect on 2-way ANOVA?

    Hello, I've run a 2 way ANOVA of my research results and got these 3 p-values: A=0.001, B=0.069, and A*B=0.167. My professor now wants me to remove the interaction effect from my analysis. Does anyone know how I can do this? In the program I am using (SigmaPlot), there is no option for removing...
  10. C

    Can someone help me with finding the P-Values for these problems?

    I have a test tomorrow and am not understanding this section very well. I need help on two problems if someone can explain how to do them! Pleaseeee! I have the answers but i want to understand HOW to do them. Obviously i don't expect anyone to do both problems for me. I know that's asking a...
  11. D

    Multiple comparison test, with ambiguous labels/ranks

    In a clinical study, I have patient's health condition labeled as grade 1, 2, or 3. Some patients are labeled as "Either 1 or 2" by the doctor, meaning the doctor considers both grade 1 and 2 as valid descriptions of the patient's health condition. When performing say a Kruskal-Wallis test...
  12. U

    Finding the p-value for two samples which are not normally distributed.

    Hello, I am doing medical research and I have gathered data for two groups of patients with different characteristics. The data for each of the groups is not normally distributed. Let's say the null hypothesis is that there are no differences between the two groups, how can I come up with the...
  13. C

    Effect Coding: p-value of reference category

    Hi, I fit a regression model with effect coded variables. I'm well aware of how to compute the value for the reference category but I have absolutely no idea how I can possibly compute the p-value or standard deviation for it. I really hope anyone can help me in this matter.... Thank...
  14. I

    Help with R an KsTest

    Hi, Some days ago i tried to do a KSTest on R, but i didn't get the answer that i needed. In Fact i didn't understand why this test gives me the same P-value for a True or False Hypotesis. I tried with an Normal distribution testing a normal distribution, and i tried a Uniform distribution...
  15. S

    Regression Model is not full rank

    Hi all, I am trying to detect relationship of crop yield at the end of the growing seasson (1 dependent variable) using amount of precipitation in May, June, July, May+June, June+july, Temperature in May etc. The problem is that I can't get p-values for many of these variables because of the...
  16. O

    Calculating probability given mean and standard deviation

    Hi I have looked around for this post on the forum but could not find one and have spent a while attempting this question: Given that X is normally distributed with mean 100 and standard deviation 9 and given a sample size of 16, compute the following: 1) mean and variance of X-dash 2)...
  17. M

    Mixed ANOVA: p-Value of within factor increases by adding a between factor...?

    Hello, I thought I'm good in math and statistics but this one is giving me a real headache...hope one of the pros here can explain/solve it... I ran a mixed ANOVA with one within and one between factor, both variables have 2 outcomes - pretty easy. Accidentally when I first did it, I...
  18. K

    Using multiple P-values

    I have a number of p-values from permutation tests I've done on my data. One p-value for each recording. Can I compile these values to test for overall significance?
  19. 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...
  20. J

    Gene expression analysis - FDR and p-values

    Hi, I'm using Affymetrix microarrays to check if there exist some differences in the gene expression of two group of animals that have been differently treated. I'm using a t-test with permutations (as my groups only have three animals and I read that it is better to use permutation if you...