+ Reply to Thread
Results 1 to 11 of 11

Thread: alternative to anova

  1. #1

    alternative to anova




    What is an alternative statistical test to anova. I have a large varience between three groups (control and two experimental). How can I determine if there is a significant difference between the means (p-value). My n=12. Thanks in advance.

  2. #2
    R must die
    Points: 25,627, Level: 96
    Level completed: 28%, Points required for next Level: 723
    Awards:
    Activity Award
    noetsi's Avatar
    Posts
    4,632
    Thanks
    303
    Thanked 734 Times in 704 Posts

    Re: alternative to anova

    What is the dependent variable? That is how is it measured.

    And why don't you want to run ANOVA (which will influence what method you replace it with since alternatives like T test are very similar in assumption).
    "..which is what 99.999% of people do so you would be wrong, but you would be wrong alongside with everyone else which somehow makes you... you know, not-so-wrong. "

  3. #3
    Points: 493, Level: 9
    Level completed: 86%, Points required for next Level: 7

    Posts
    5
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Re: alternative to anova

    Dependent variable is transcriptional activity for a reporter assay. I ran anova but the variance for my groups are very different. I read that you should not use anova if the variances between groups not similar.

    Varience of data:
    Control = <1
    Group 1 = 32
    Group 2 = 19

  4. #4
    Beep
    Points: 62,703, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Discussion EnderPosting AwardCommunity AwardMaster TaggerFrequent Poster
    Dason's Avatar
    Location
    Ames, IA
    Posts
    11,246
    Thanks
    265
    Thanked 2,188 Times in 1,867 Posts

    Re: alternative to anova

    When you say n = 12 do you mean you have 12 subjects in each group or 12 subjects total (4 in each group?)

  5. #5
    Points: 493, Level: 9
    Level completed: 86%, Points required for next Level: 7

    Posts
    5
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Re: alternative to anova

    I have data from 12 separate experiments. Each experiment contains a single data value for each of 3 groups (1 control and 2 experimental). So I have a total of 36 data points; 12 data points for each group.

  6. #6
    R must die
    Points: 25,627, Level: 96
    Level completed: 28%, Points required for next Level: 723
    Awards:
    Activity Award
    noetsi's Avatar
    Posts
    4,632
    Thanks
    303
    Thanked 734 Times in 704 Posts

    Re: alternative to anova

    The inequality of the population variances can be assessed by examination of the relative size of the sample variances, either informally (including graphically), or by a robust variance test such as Levene's test. (Bartlett's test is even more sensitive to nonnormality than the one-way ANOVA's F test, and thus should not be used for such testing.) The effect of inequality of variances is mitigated when the sample sizes are equal: The F test is fairly robust against inequality of variances if the sample sizes are equal, although the chance increases of incorrectly reporting a significant difference in the means when none exists. This chance of incorrectly rejecting the null hypothesis is greater when the population variances are very different from each other, particularly if there is one sample variance very much larger than the others.
    The effect of inequality of the variances is most severe when the sample sizes are unequal. If the larger samples are associated with the populations with the larger variances, then the F statistic will tend to be smaller than it should be, reducing the chance that the test will correctly identify a significant difference between the means (i.e., making the test conservative).
    How different are your populations (your group) variances from each other? And how similar are their sample sizes?

    Did you run the Levene test and it showed they were in fact signficantly unequal?

    http://www.basic.northwestern.edu/st..._ass_viol.html
    "..which is what 99.999% of people do so you would be wrong, but you would be wrong alongside with everyone else which somehow makes you... you know, not-so-wrong. "

  7. The Following User Says Thank You to noetsi For This Useful Post:

    deardirestraits (12-16-2011)

  8. #7
    TS Contributor
    Points: 10,299, Level: 67
    Level completed: 63%, Points required for next Level: 151
    Karabiner's Avatar
    Location
    Schalke 04, Germany
    Posts
    1,570
    Thanks
    28
    Thanked 388 Times in 370 Posts

    Re: alternative to anova

    Quote Originally Posted by deardirestraits View Post
    I have data from 12 separate experiments. Each experiment contains a single data value for each of 3 groups (1 control and 2 experimental).
    Are the groups really independent? Couldn't this be a repeated-measures design
    (12 "subjects", 3 levels)? What is the nature of the intervention/experiment
    and of the data points? Could you explain it in a bit more detail?

    Kind regards

    K.

  9. #8
    Beep
    Points: 62,703, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Discussion EnderPosting AwardCommunity AwardMaster TaggerFrequent Poster
    Dason's Avatar
    Location
    Ames, IA
    Posts
    11,246
    Thanks
    265
    Thanked 2,188 Times in 1,867 Posts

    Re: alternative to anova

    Well if it's 12 different experiments I don't think there would be much of a problem with independence

  10. #9
    Points: 493, Level: 9
    Level completed: 86%, Points required for next Level: 7

    Posts
    5
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Re: alternative to anova

    The Levene test certainly sounds like a good start. If I find that my variance is significantly different where do i go from there? What is the right test?

    It might be appropriate to mention that variation between my control and experimental groups is large because of the sensitivity of the machine that I collect my data from. The ratio of the means between the two experimental groups is usually consistent. If this makes sense or is helpful in your assisting me great. If not forget that I mentioned it.

    I listed the variances in post 2. Sample sizes are the same for all groups.

  11. #10
    R must die
    Points: 25,627, Level: 96
    Level completed: 28%, Points required for next Level: 723
    Awards:
    Activity Award
    noetsi's Avatar
    Posts
    4,632
    Thanks
    303
    Thanked 734 Times in 704 Posts

    Re: alternative to anova

    If you have unequal variances I would imagine that you would have heteroskedacity so many forms of regression would have problems as would t test. Weighted least squares or a transformation of the data might work, although I suspect some form of ANOVA is still your best bet. But it would be a more complex design than I work with.
    "..which is what 99.999% of people do so you would be wrong, but you would be wrong alongside with everyone else which somehow makes you... you know, not-so-wrong. "

  12. #11
    Points: 493, Level: 9
    Level completed: 86%, Points required for next Level: 7

    Posts
    5
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Re: alternative to anova


    Thanks for the help!

+ 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