+ Reply to Thread
Results 1 to 11 of 11

Thread: comparing extremes of an independent variable

  1. #1
    Points: 18, Level: 1
    Level completed: 35%, Points required for next Level: 32

    Posts
    4
    Thanks
    2
    Thanked 0 Times in 0 Posts

    comparing extremes of an independent variable




    Dear all,

    I have been cracking my head for 2 weeks but i havent been able to figure out this, so i decided to ask for help.

    I have done a regression between my independent and independent variable and found nothing.
    Now my supervisor wants me to find out if what i wanted to find, can only be found at the extremes.

    So participants with the lowest scores (10% left) and participants with the highest scores (10% right).

    My supervisor didnt give me much help, she only said something about using ANOVA?

    I hope someone can help me.

    kind regards

    Niccolo

  2. #2
    Points: 4,664, Level: 43
    Level completed: 57%, Points required for next Level: 86
    kiton's Avatar
    Location
    Corn field
    Posts
    234
    Thanks
    47
    Thanked 51 Times in 46 Posts

    Re: comparing extremes of an independent variable

    Quote Originally Posted by niccolo View Post
    Dear all,

    I have been cracking my head for 2 weeks but i havent been able to figure out this, so i decided to ask for help.

    I have done a regression between my independent and independent variable and found nothing.
    Independent and dependent variables, I assume. As otherwise, you are indeed likely to find nothing

    Quote Originally Posted by niccolo View Post
    Now my supervisor wants me to find out if what i wanted to find, can only be found at the extremes.

    So participants with the lowest scores (10% left) and participants with the highest scores (10% right).

    My supervisor didnt give me much help, she only said something about using ANOVA?
    What you can try here is run a quantile regression (QR) -- one that would allow you to estimate the impact of your predictor on the DV in the lower (e.g., 10th) or higher (e.g., 90th) percentiles of the distribution, if that is what you are looking for.

    Check this paper to get a sense of what QR is all about: Cade, B. S., & Noon, B. R. (2003). A gentle introduction to quantile regression for ecologists. Frontiers in Ecology and the Environment, 1(8), 412-420.

  3. The Following User Says Thank You to kiton For This Useful Post:

    niccolo (08-04-2016)

  4. #3
    Omega Contributor
    Points: 38,374, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    6,998
    Thanks
    398
    Thanked 1,186 Times in 1,147 Posts

    Re: comparing extremes of an independent variable

    Can you tell use more about your data. Do you have two continuous variables or if not how are they formatted?


    Have you plotted you data at all to see if there may be trends or possible visual differences. Visualizing data is important in figuring out which direction to go.
    Stop cowardice, ban guns!

  5. #4
    TS Contributor
    Points: 12,227, Level: 72
    Level completed: 45%, Points required for next Level: 223
    rogojel's Avatar
    Location
    I work in Europe, live in Hungary
    Posts
    1,470
    Thanks
    160
    Thanked 332 Times in 312 Posts

    Re: comparing extremes of an independent variable

    Quote Originally Posted by niccolo View Post

    My supervisor didnt give me much help, she only said something about using ANOVA?

    I hope someone can help me.

    kind regards

    Niccolo
    Hi,
    what your supervisor might have in mind is to build two groups, LOW and HIGH say, and to run an ANOVA with the two groups (actually a simple t-test is enough in this case).
    regards

  6. #5
    Points: 18, Level: 1
    Level completed: 35%, Points required for next Level: 32

    Posts
    4
    Thanks
    2
    Thanked 0 Times in 0 Posts

    Re: comparing extremes of an independent variable

    Quote Originally Posted by hlsmith View Post
    Can you tell use more about your data. Do you have two continuous variables or if not how are they formatted?


    Have you plotted you data at all to see if there may be trends or possible visual differences. Visualizing data is important in figuring out which direction to go.
    I will elaborate more yes, thx for the answers!

    I have 5 independant variables (personality traits) and my dependant variable is Telomere length. All continous.

    Doing a multiple regression i found that my independant variables had no significant effect on my dependant varable. Now i need to figure out if the effects do appear when looking at the extremes.

    Hope this makes it more clear?

    Im going to read that QR thing, first time i hear about it, thx!

  7. #6
    Omega Contributor
    Points: 38,374, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    6,998
    Thanks
    398
    Thanked 1,186 Times in 1,147 Posts

    Re: comparing extremes of an independent variable

    So your description still reads a little weird. So you have 5 different continuous variables, correct? Do you want to see if all of these may differ by extremes?


    What is your sample size?


    You may want to strategically break the trait in categories, then make lowest level the reference group for comparisons.


    So you think traits predict lengths. I would wonder in general about that hypothesis and in addition wonder if you have the independent and dependent variables actually switched?
    Stop cowardice, ban guns!

  8. #7
    Points: 18, Level: 1
    Level completed: 35%, Points required for next Level: 32

    Posts
    4
    Thanks
    2
    Thanked 0 Times in 0 Posts

    Re: comparing extremes of an independent variable

    Quote Originally Posted by hlsmith View Post
    So your description still reads a little weird. So you have 5 different continuous variables, correct? Do you want to see if all of these may differ by extremes?


    What is your sample size?


    You may want to strategically break the trait in categories, then make lowest level the reference group for comparisons.


    So you think traits predict lengths. I would wonder in general about that hypothesis and in addition wonder if you have the independent and dependent variables actually switched?
    the sample size is substantial, is almost 10 thousand participants.

    maybe giving a concrete example would help to explain myself.

    Scores on a persality (neuroticism) may have a negative effect and thus shortening the length of the telomeres. Because i havent found any statistical significance during my regression. I postulate that the effect of personality traits may only be seen when u look at the extremes. And thus comparing lowest 10% and highest 10% of the scores of said trait onto telomere length.

    This exact thing, i have to do with all 5 personality traits. while taking the age of my participants into consideration.

    all my variables are continuous (dependant and independant ones)

    the english lenguage isnt my forte, i hope i explained myself a bit better this time

  9. #8
    Omega Contributor
    Points: 38,374, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    6,998
    Thanks
    398
    Thanked 1,186 Times in 1,147 Posts

    Re: comparing extremes of an independent variable

    That did help.


    Quantile regression deals with grouping the dependent variable, which you want to chop up your independent variable. You can chop up your IV and control for age, you just need to let people know if you disseminate results that this was a post hoc analysis. I am not familiar with multivariate regression, but I believe you want to go that route because you are examining multiple things against the dependent variable. So yeah, go ahead and dissect the middle values and run your model with all chopped up variables!
    Stop cowardice, ban guns!

  10. The Following User Says Thank You to hlsmith For This Useful Post:

    niccolo (08-04-2016)

  11. #9
    Points: 18, Level: 1
    Level completed: 35%, Points required for next Level: 32

    Posts
    4
    Thanks
    2
    Thanked 0 Times in 0 Posts

    Re: comparing extremes of an independent variable

    Quote Originally Posted by hlsmith View Post
    That did help.


    Quantile regression deals with grouping the dependent variable, which you want to chop up your independent variable. You can chop up your IV and control for age, you just need to let people know if you disseminate results that this was a post hoc analysis. I am not familiar with multivariate regression, but I believe you want to go that route because you are examining multiple things against the dependent variable. So yeah, go ahead and dissect the middle values and run your model with all chopped up variables!
    Thank you! is there any way to achieve that on SPSS? Because i read that QR is done in R (which i know little to nothing about)

  12. #10
    Omega Contributor
    Points: 38,374, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    6,998
    Thanks
    398
    Thanked 1,186 Times in 1,147 Posts

    Re: comparing extremes of an independent variable

    You don't want to do QR.
    Stop cowardice, ban guns!

  13. #11
    Points: 4,664, Level: 43
    Level completed: 57%, Points required for next Level: 86
    kiton's Avatar
    Location
    Corn field
    Posts
    234
    Thanks
    47
    Thanked 51 Times in 46 Posts

    Re: comparing extremes of an independent variable


    hlsmith is right in that QR "chops" the DV, not the IVs. As such, if I understood his proposition correctly, you can "chop-out" the middle values of your independent variable(s) and keep only those that are at "extremes". For example, assuming the values of your IV(s) range from 1 to 100, recode 11 through 89 as missing values (or use -if-) -- then run the regression using this "chopped" variable(s). Note, your sample size is likely to decrease but having 10k cases you'll have plenty left, I guess.
    Last edited by kiton; 08-04-2016 at 08:02 PM.

+ 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