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  1. hlsmith

    Is there a test for omitted variable bias?

    If there are two groups of kids, one gets a computer, one doesnt. Later you see which group was more likely to pass a test. Well was it the computer or that one group had a disproportionate high number of honors students. So the computer could have helped or it was the kids would have done...
  2. hlsmith

    Partial reggression plots

    Well you can use LOESS, but since you mentioned partial, GAMs allow you to throw in covariates. I run mostly logistic reg, so here is an example for that:
  3. hlsmith

    P values versus slope

    Yeah, but in every instance you are making a decision based on a binary rule and why does 0.05 matter instead of 0.1 or if you have a huge dataset, 0.001? They are just making a bunch of incremental hypotheses. That would probably make a good paper, how many statistical test get ran when...
  4. hlsmith

    regression degrees of freedom

    When you do a PROC CONTENTS, how is it defining these variables? If they are numbers, you gotta let the program know or if using PROC REG use created dummies - I know you know how to do that. I remember you working with me once on an option in PROC REG and using dummies.
  5. hlsmith

    Competing risk COX in SPSS

    Yeah, I primarily use SAS for Cox, but I am truly sure it can be done in R. Well in 1995 it couldn't do it:!topic/comp.soft-sys.spss/oQwg37MSTfo I wonder if there is a SPSS Help Forum you can consult or just give the company a call.
  6. hlsmith

    Is there a test for omitted variable bias?

    If you do not randomize the exposure and also control for extraneous factors you can never truly know if an omitted variable may be impacting the outcome. With enough evidence and causal assumptions, you can presume a causal relationship, but you just need to posit a confounder could be...
  7. hlsmith

    regression degrees of freedom

    So if I remember proc reg doesn't have the class statement, so you have to dummy code them right?! Which variables should be treated as categorical?
  8. hlsmith

    Competing risk COX in SPSS

    Not a SPSS user, but I would imagine it should be available? Sorry I don't have specifics, just acknowledging you post - not a tremendous amount of SPSS user currently on this forum - but keep the posts coming.
  9. hlsmith

    Mixed model an linear model gave the same results

    Typically if you think you have a multilevel model, but controlling for groups does not explain any additional variability (ICC), and its not a power issue (sample size), people will revert back to a OLS model and use sandwich SE estimators for simplicity and sandwich for staving off type I errors.
  10. hlsmith

    Partial reggression plots

    When I test a continuous variable for linearity in the model, I usually just use a SAS gam model (I think gampl, etc.) and look at the plotted relationship and how many if any knots there are on it.
  11. hlsmith


    Welcome to the forum Grant. Not sure why your music is pretentious- its just music. We look forward to your questions and posts!
  12. hlsmith

    Is there a test for omitted variable bias?

    You don't know, what you don't know. If you do know you are missing a variable of interest you can do things like Bayesian or monte carlo simulation to try and figure our it possible effect.
  13. hlsmith

    Is there a test for omitted variable bias?

    There is no test. You can try to quantify how large a lurking variable would have to be to negate results - you can do this via external or internal record-level sensitivity analysis.
  14. hlsmith

    Hey to the group

    Welcome to the forum. I see you posted this twice, so I will direct people to the longer description: Posting twice is a faux pas and that it can results in multiple people working on the same thing...
  15. hlsmith

    Help! Three years pre vs three years post

    Please provide more information, such are does each student has 6 observation or not. Also, what is the sample size and distribution of scores? Did people get 100% on the exam?
  16. hlsmith

    ARIMA model transformation

    Well this is a completely different set up than your first post. We typically ask OP's to show initial due diligence before just giving out answers to possible school work. a). what terms in the model and was differencing used? b.) is the Dt-1 a unit root term? c + d) plug data into...
  17. hlsmith

    ARIMA model transformation

    What do you actually have in front of you. Were you given this scenario or do you have an actual data series? Can't recall the rule behind differencing logs but it may be converted to division of something of that nature. Those rules are pretty searchable. However, if I have say the value 5 and...
  18. hlsmith

    What are the statistical tests need to be done before backward multiple regression?

    You don't need to perform test before regression - those tests can be misleading (don't address confounders, collinearity, mediation) and descriptive in nature. You just run your regression given your content expertise in the area and knowledge of the relationships between terms. However...
  19. hlsmith

    What are all the types of Sparsity?

    Also, do you have a particular context you are referencing for sparsity? Say more variables than observations. So are you trying to find the best subset of variables or you could have sparsity given 50 people and 2 covariates in logistic regression - where regularized or exact approaches my be...
  20. hlsmith

    Sample Size for Variable Data

    One-sample ttest is fine and typically used to compare a sample to a constant value, so i dont get your question. How about you provide a full example to convey your question! Thanks! @Miner heads up this seems like its going to be industrial or quality related.