+ Reply to Thread
Results 1 to 7 of 7

Thread: Multiple Regression theory

  1. #1
    Points: 787, Level: 14
    Level completed: 87%, Points required for next Level: 13

    Posts
    55
    Thanks
    2
    Thanked 4 Times in 4 Posts

    Multiple Regression theory




    Hey guys I'm not too good with the logic of multiple regression so I'd like some enlightenment on the following query.

    I'm running a multiple regression on the following;

    IV1: Protective factors
    IV2: Risk factors
    IV3: IAT score

    DV: Number of Suicide attempts

    Now my hypothesis is that each IV will contribute significantly to the change in R-squared.

    BUT only the Risk factors and IAT score are positively correlated with the number of suicide attempts. Protective factors is actually negatively correlated.

    So the question is, can I use the multiple regression to answer my hypothesis?

    Intuitively I feel that if I include a negatively correlated IV it is not going to help me predict the DV at all. If I'm wrong could someone please give an explanation.

    Much appreciated!

  2. #2
    Point Mass at Zero
    Points: 13,828, Level: 76
    Level completed: 45%, Points required for next Level: 222
    ledzep's Avatar
    Location
    Berks,UK
    Posts
    684
    Thanks
    188
    Thanked 143 Times in 139 Posts

    Re: Multiple Regression theory

    Hi durantz, interesting question.

    Now my hypothesis is that each IV will contribute significantly to the change in R-squared.
    Is this your null hypothesis? How would you judge whether the change in R-Squared is significant or not? Drop of 2%, 5%? (Never seen hypothesis defined in terms of R-2).

    The negative correlation makes sense, as if there are more protective factors (support from friends and family etc..)around the patient, the less likely they are to commit a suicide.
    I think it would be wrong to exclude this as this is an important variable that you need to take into account.
    As you've just 3 IV, I think you can use all of these 3 variables to perform a multiple regression and assess their significance in the presence of other variables in the model.

    In any case, if you have more IV in the model, it should help in predicting better.
    Oh Thou Perelman! Poincare's was for you and Riemann's is for me.

  3. #3
    Points: 787, Level: 14
    Level completed: 87%, Points required for next Level: 13

    Posts
    55
    Thanks
    2
    Thanked 4 Times in 4 Posts

    Re: Multiple Regression theory

    Thanks for that ledzep.

    To be specific I'm doing a hierarchical multiple regression.

    In SPSS it calculates the F-ratio associated with the change in R-squared, thus telling me whether or not it is significant.

    I will attach my results table for the regression if that helps. As you will see in both steps of the regression only risk factors has a significant standardised beta. From this results table I am going to conclude that only 'risk factors' contributes significantly to the prediction of number of suicide attempts.

    So what you're saying is that it doesn't matter if you include positively and negatively correlated IVs in the regression? My intuitions just had me thinking you'd only want to include variables that are ALL positively correlated or ALL negatively correlated. But now that I think about it that seems wrong.

    Edit: just noticed my table is mislabelled. It should be No. of previous suicide attempts.
    Attached Images  
    Last edited by durantz; 04-05-2012 at 12:49 AM. Reason: clarification

  4. #4
    TS Contributor
    Points: 17,749, Level: 84
    Level completed: 80%, Points required for next Level: 101
    Karabiner's Avatar
    Location
    FC Schalke 04, Germany
    Posts
    2,540
    Thanks
    56
    Thanked 640 Times in 602 Posts

    Re: Multiple Regression theory

    Now my hypothesis is that each IV will contribute significantly to the change in R-squared.
    a) Each predictor is associated with number of suicide attemts (three univarite analyses).
    b) the three predictors jointly can predict nimber of suicide attempts (model R in multiple regression).
    c) each predictor in the model independently contributes to the prediction (as can be seen by significant regression weights in the multiple regression).
    Intuitively I feel that if I include a negatively correlated IV it is not going to help me predict the DV at all. If I'm wrong could someone please give an explanation.
    Oops. What concept of correlation/negative correlation do you have in mind?
    Negative correlation does not decrease prediction. Change "number of predictive factors"
    (say, now numbers between 0 and 11) into "number of lacking protective factors" (say, how
    many of 20 factors were lacking) then you'l have a positive correlation while conceptually
    there hasn't been changed anything.

    Kind regards

    K.

  5. #5
    Points: 787, Level: 14
    Level completed: 87%, Points required for next Level: 13

    Posts
    55
    Thanks
    2
    Thanked 4 Times in 4 Posts

    Re: Multiple Regression theory

    Thanks a lot Karabiner! Those hypotheses are very helpful.

    I should be fine now.

  6. #6
    Points: 651, Level: 13
    Level completed: 2%, Points required for next Level: 49

    Location
    Groningen, Netherlands
    Posts
    43
    Thanks
    2
    Thanked 2 Times in 2 Posts

    Re: Multiple Regression theory

    A small addition:

    - Very often, if additional independent variables are included, R-2 will increase. Normally, I always look at the adjusted R-2 (in spss) to see whether an addidtional variable makes sense, because the adjusted R-2 accounts for the number of variables included.

    - Second, R-2 measures how much of the variation in your dependent variable can be explained by your independent variables, so.. a significant negative correlation is actually good and will enhance R-2.

    just to make things a bit more clear

  7. #7
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: Multiple Regression theory


    Quote Originally Posted by Eyecatcher View Post
    A small addition:

    - Very often, if additional independent variables are included, R-2 will increase.
    And by "very often" they mean that it's actually impossible for R^2 to decrease when you add a predictor.
    I don't have emotions and sometimes that makes me very sad.

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats