+ Reply to Thread
Results 1 to 2 of 2

Thread: T-Test and unequal sample sizes

  1. #1
    Points: 2,548, Level: 30
    Level completed: 66%, Points required for next Level: 52

    Posts
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    T-Test and unequal sample sizes




    I am currently interning for a manufacturing company that makes knee implants. I was asked to do a T-test on some test data. There was sterilization testing done on each product the company makes and I was asked to compare the results of each product to their main product, the Femur, for the T-test. I know almost nothing about statistics, I had to google T-test to figure out what it was.

    The only program available to use is Excel XP, for some reason I can't install the data analysis toolpack after going to Tools>Add Ins. Because of this, all I could do is use the TTEST equation. I did one T-test for each product using its result as the 2nd array, the 1st array is always the Femur. I also used 2-tail and unequal variance type.

    My problem is that the Femur has about 40 samples, but some of the other parts have 10-30 samples. I can get a P value after entering the T-Test with unequal sample sizes, but are my results going to be correct? Should I make sure I have equal sample sizes by omitting some of the Femur samples? If so, what would be a proper way to omit samples?

    Thanks in advance for any help.

  2. #2
    TS Contributor
    Points: 10,600, Level: 68
    Level completed: 38%, Points required for next Level: 250
    CowboyBear's Avatar
    Location
    New Zealand
    Posts
    1,489
    Thanks
    63
    Thanked 253 Times in 186 Posts

    A t test can still be performed with unequal sample sizes; but the smaller sub-sample will limit the statistical power of the test. With just 10 cases in some of your subsamples, the power to detect "statistically significant" differences will be very very low - differences will only be "statistically significant" if the group means are very different. There's no statistical cure for this problem, per se - you should probably see if you can obtain larger samples, or simply report group mean differences rather than attempting inferential testing.

    T-test assumptions here.

+ Reply to Thread

           




Similar Threads

  1. T-test and large but unequal sample sizes
    By adelwich in forum Statistics
    Replies: 2
    Last Post: 04-05-2011, 04:03 PM
  2. Replies: 2
    Last Post: 02-19-2011, 02:35 AM
  3. unequal sample sizes
    By Ali59 in forum Statistics
    Replies: 0
    Last Post: 11-10-2009, 09:07 AM
  4. unequal sample sizes
    By janse030 in forum Psychology Statistics
    Replies: 0
    Last Post: 10-08-2008, 10:54 AM
  5. Unequal sample sizes in JMP?
    By trmstat in forum Other Software
    Replies: 0
    Last Post: 07-31-2008, 06:58 PM

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