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Thread Subject:
anova1

Subject: anova1

From: Kristina

Date: 14 Oct, 2013 11:38:06

Message: 1 of 3

I have 6 images that look almost the same, there are some differences though. I've withdrawn 5 of images from the first one and I'm trying to use anova1 to see if they are from the same population but I get strange results. Figure 2 shows red '+' signs (the actual values of my data) and it is from 0 to 255. And there is a blue line at 0. What am I doing wrong?

Subject: anova1

From: Tom Lane

Date: 16 Oct, 2013 22:06:56

Message: 2 of 3

> I have 6 images that look almost the same, there are some differences
> though. I've withdrawn 5 of images from the first one and I'm trying to
> use anova1 to see if they are from the same population but I get strange
> results. Figure 2 shows red '+' signs (the actual values of my data) and
> it is from 0 to 255. And there is a blue line at 0. What am I doing wrong?

I don't understand exactly what you are doing. However, here is something
that will reproduce what you saw:

x = zeros(1000,5);
x(ceil(5000*rand(100,1))) = floor(255*rand(100,1));
anova1(x)

Now, I understand this is not what you have done. But I have data mostly at
or near zero, with a relatively small proportion of points taking other
values as high as 255. This may describe what your image matrices look like.
If you make a box plot of them (your Figure 2), you should see that the
quartiles and medians are drawn as blue lines right near zero, and the other
values are outliers drawn as red plus signs above that.

The other figure will contain your anova table. Normally anova is performed
on continuous data. You appear to have coarse data with lots of zero values.
I don't know if anova would work well for that.

I'd have to understand more about your problem to suggest anything.

-- Tom

Subject: anova1

From: Kristina

Date: 17 Oct, 2013 18:36:05

Message: 3 of 3

"Tom Lane" <tlane@mathworks.com> wrote in message <l3n2m0$pj9$1@newscl01ah.mathworks.com>...
> > I have 6 images that look almost the same, there are some differences
> > though. I've withdrawn 5 of images from the first one and I'm trying to
> > use anova1 to see if they are from the same population but I get strange
> > results. Figure 2 shows red '+' signs (the actual values of my data) and
> > it is from 0 to 255. And there is a blue line at 0. What am I doing wrong?
>
> I don't understand exactly what you are doing. However, here is something
> that will reproduce what you saw:
>
> x = zeros(1000,5);
> x(ceil(5000*rand(100,1))) = floor(255*rand(100,1));
> anova1(x)
>
> Now, I understand this is not what you have done. But I have data mostly at
> or near zero, with a relatively small proportion of points taking other
> values as high as 255. This may describe what your image matrices look like.
> If you make a box plot of them (your Figure 2), you should see that the
> quartiles and medians are drawn as blue lines right near zero, and the other
> values are outliers drawn as red plus signs above that.
>
> The other figure will contain your anova table. Normally anova is performed
> on continuous data. You appear to have coarse data with lots of zero values.
> I don't know if anova would work well for that.
>
> I'd have to understand more about your problem to suggest anything.
>
> -- Tom

Thank you for the answer, Tom!

Yes, I get that kind of box plot. Okay, I can try and explain my problem. I have 6 images, one is original and 5 are slightly changed in a comparison to the original image. I've subtracted the 5 changed images from the original one and got 5 populations. And I'd like to know if these 5 slightly changed images (the methods that made them different) comes from the populations with the same mean...

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