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How to interpret PCA

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Jin Woo PARK
Jin Woo PARK on 7 Sep 2020
Answered: the cyclist on 7 Sep 2020
Hi, I was trying a principal component analysis and I'd like to get some help
First, here is a table that shows measured concentrations of dopamine (DA), 3,4-hydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in mice urine after 2 hours of brain electric stimulus. The stimulus intensity were control in 3 mice, 100 μA in 4 mice, and 200 μA in 4 mice.
Using pca function, How can I interpret that which hormone is the most significant?
Also, I'd like to draw a scatter plot in different colors in each group (control, 100, 200)?

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Star Strider
Star Strider on 7 Sep 2020
How are you using pca with your data?
Jin Woo PARK
Jin Woo PARK on 7 Sep 2020
I tried using pca function typing as
[coeff_2hours,score_2hours,latent_2hours,explained_2hours,mu_2hours]=pca(x2hours)
and here are the output results
coeff_2hours=
0.079673 0.528817 0.844988
0.418385 0.751662 -0.50986
0.904769 -0.39415 0.161362
score_2hours=
-5.04709 -8.41625 -2.15417
46.53202 6.334792 0.147732
-53.3088 1.198444 4.712148
-0.68473 4.310732 -3.02132
-30.1071 2.136703 2.991445
47.59406 -6.29931 3.21377
-25.753 -0.84886 -3.01205
3.155725 -2.33881 1.021516
20.26302 1.733989 -1.06366
-20.2205 -0.14942 -4.20901
17.57651 2.337988 1.373598
latent_2hours=
1000.621
18.99142
8.612187
explained_2hours=
97.31541
1.847012
0.837579
mu_2hours=
14.38647 27.68305 61.08517
Image Analyst
Image Analyst on 7 Sep 2020
You forgot to attach x2hours. Please do so
save('answers.mat', 'x2hours');
Also, I don't know what you plotted but I'm not sure I see any point in using PCA since your data looks like a shotgun blast - totally uncorrelated.

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Answers (1)

the cyclist
the cyclist on 7 Sep 2020
@Jin Woo:
If search this forum for cyclist and pca, you will find a few question/answers where I explain a lot about the interpretation of PCA output. Here are a couple you might want to look at:

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