turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Find a Community

- Home
- /
- SAS Programming
- /
- SAS Procedures
- /
- Mean or median

Topic Options

- RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-25-2017 02:26 PM

I am comparing 2 groups in some baseline measures. One of the groups is rather small (n=6) while the other is moderate at n=20. Should I use the mean or median in my table and my group comparisons? My concern is, with a sample size of 6 in 1 group, the wilcoxon test just seems less powerful than a t-test.

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Melk

09-25-2017 03:32 PM - edited 09-25-2017 03:34 PM

To tell you the truth, the decision on whether or not to use a mean or a median depends on what you intend to do with the statistic (which you haven't told us) and also whether or not the distribution of the data is skewed or not.

If the distribution is not skewed, and is relatively symmetric, the mean and the median ought to give very similar answers.

Regarding the Wilcoxon test, I believe it is ALWAYS less powerful than the t-test ... but I guess I haven't actually seen that proved either. Maybe Wilcoxon is less powerful for relatively symmetric distributions, and more powerful for very skewed distribtuions? I'm guessing...

But the answer depends on the symmetry or skewness of your distribution, and not really on the sample size.

--

Paige Miller

Paige Miller

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to PaigeMiller

09-25-2017 07:59 PM

I will be comparing baseline values between the 2 groups using a 2 sample t test or mann whitney u as appropriate.

The issue for me here is that with N=6, it is difficult to assess symmetry and skewnesss, so I usually resport to non-parametric methods, but I wondered if anyone else had other suggesstions.

- Mark as New
- Bookmark
- Subscribe
- RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Melk

09-26-2017 08:32 AM

I probably could have written a clearer message. What I should have said is that you want to judge the symmetry or skewness of the populations; it really doesn't matter what the symmetry or skewness of the sample is.

Now, it may be that you don't have any idea about the population, but for some populations you might have a good idea that the population is skewed, or not.

--

Paige Miller

Paige Miller