# odds ratio

1. ### How to compare 2 ORs from different regression models.

I created a logistic regression model to predict an outcome of depression vs. no depression. There are several variables in the model including gender. I then stratified the population and created 2 logistic regression models (one for women and one for men) because of interactions between gender...
2. ### Chi Sqaure and odds ratio help

Hi all, I was wondering - what's the relationship between chi square and odds ratio? To me it makes sense that these two values are fixed- i.e., if one value changes, the other will. Is it possible to observe the same odds ratio in two different tests with different sample sizes but get a...
3. ### McNemar's test post-hoc power analysis problem when odds ratio=0

I need to do post-hoc power analysis for a McNemar's test (using G*power), and am having trouble getting results. One of the discordant pairs is 0, therefore the odds ratio is zero, and it seems that power cannot be calculated using an odds ratio of 0. Is there any way around this...
4. ### Understanding odds ratios and probability

While looking some lecture notes on odds ratios of genomic tests I came across this formula: P(trait | A) = Odds(A)/[1+Odds(A)] I'm confused. Say that the trait is "having a heart attack" and A is the genotype of some gene. Then according to this formula if I know the odds ratio of A on...
5. ### Chi square observed frequencies help please

Hi there If anyone could help me , with what is probably a really simple/stupid question, I would be so grateful! It is not through lack of trying and reading to understand this- but I'm still really confused. I have done a chi square 2x3, the assumptions were met as all expected...
6. ### Odds ratios lower than 1 for continous variable

Lets says you want to check the effect of age on a specific event. In the univariate model : event = age, the odds is significantly lower than 1 which seems to show a 'protective impact' of age on this event (age increase -> probablity of event decrease) However, after checking, average of...
7. ### Combining two ORs with the same control group

Hi everybody. I am doing a meta-analysis of observational studies. As the disease I am working on has different stages, some of the studies reported ORs(95%CI) for each stage separately in comparison to a single (shared) control population. I wonder if we can combine these two ORs (and their...
8. ### How to get OR in STATA after xtlogi..,fe (multilevel)

Hi guys I have been trying to get the odds ratios for my logistic multilevel regression with a fe estimator. I type my regression and then the post estimation command xtlogit, or But, the odds ratio I get for my primary X is way too big. It's 90,0. The variable do explain a lot of my...
9. ### Logistic regression controlling for variables vs. layer in crosstabs

Hi everyone, I would like to know how SPSS controls for variables in logistic regression in order to report the correct "controlled" OR. The specific case which bothers my is as follows: Lets say I have one IV tumor size which is either small tumor size or large tumor size the other IV...
10. ### Analysis and Post-hoc for Ordinal Variables

My main questions are; 1) For a Chi goodness of fit test, which effect size do you use? I am being told Cramer's V, Phi, Omega and W! (There seem to be a lot more answers for a Chi association test, but not for a Chi goodness of fit) 2) Can you use an Odds Ratio with a Chi goodness of fit...
11. ### 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)...
12. ### cumulative odds ratios - additive or exponential?

I have run some regression models that examine the effect of variable X (a 15 point continuous scale) on Y (a binary variable - didn't perform/did perform a particular behaviour) using logistic regression. For the sake of this example, let’s say that the OR is 1.08. I can argue that for each...
13. ### Logistic Regression (very small proportion of 'yes')

Hi Everyone, I am working on a logistic regression problem (injury [y/n] predicted by air temperature and physical training program). Problem is that only 1.2% of the entire 10000 sample had an injury, and this 1.2% is almost equally distributed between the 2 pt programs. I am investigating...
14. ### Working out risk factors for a medical complication?

Hi All - HELP! I have a large dataset on women in labour, and I'm interested in finding out risk factors for a particular complication of labour. The complication is either there, or not there. I also have lots of information on possible risk factors for the complication, e.g.: length of...
15. ### Relative Risk Ratio (RRR) Analysis with a Continuous Predictor

Hi, I am hoping that someone can help me with a relative risk ratio analysis. I'm trying to assess the ability of a continuous variable to predict a categorical outcome (the base group - Y) relative to other possible outcomes. The RRR analysis gave me the RRR for the likelihood of outcome A...
16. ### odds ratio to proability

Let's say I have an odds ratio from logistic regression that's 1.4:1 for males:females. How can I get probabilities back out of this? The formula for odds ratio is \frac{\frac{p_1}{1-p_1}}{\frac{p_2}{1-p_2}}
17. ### Odds & Risk Ratio

Hi, Just wondering if In a Prospective Case-Control 'risk factor' analysis with a relatively rare outcome of interest (6.7%). Does the Odds Ratio produced from 2x2 tables equal or roughly approximate to the Risk Ratio? If so would i be justified in reporting my Odds Ratio as a Risk Ratio...
18. ### Logistic Regression with Continuous Predictor Variable

Hi, Just a quick question... For my Honours project I am running a risk factor analysis, therefore I've been using logistic regression. When using categorical predictors this whole process hasn't been a problem. However I have one variable that is 'Continuous' & this is giving me some...
19. ### Exp(b) in multinomial logistic regression: odds or risk ratio

Hi everyone This is going to be a ridiculously simple question, but I'm really struggling to find the answer. I've done a multinomial logistic regression using SPSS version 18 and am interpreting the results: I'm getting conflicting information about whether the Exp(b) parameter estimate...
20. ### What are the odds?

Spotted in a Lancet article from 2011: I was curious to see how they got such an extraordinary odds ratio and confidence interval. In the article, under "Statistical analysis" [sic] it says "Microsoft Excel was used for all analyses" but doesn't explain the odds ratio. Disappointing. (The...