Programming the statistical procedures from SAS

How can I assess the model through the diagnostics panel?

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Contributor
Posts: 48

How can I assess the model through the diagnostics panel?

[ Edited ]

The simple linear regression model is E(Yi) =α+β Xi 

When the regression is done, I get the diagnostics panel as below. I was required to access the model quality through the diagnostics panel and I also see some explanation through SAS support:

http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_reg_sect004....

 

but It is still not very understandable. I hope someone can expain to me through the following example. Thanks in advance.

 

 

2015-11-22_155321.png

2015-11-22_155338.png

Super User
Posts: 18,601

Re: How can I access the model quality through the diagnostics panel?

I think you mean assess, not access.

One of the assumptions for linear regression is:
Errors are normally distributed.

If you look at the histogram in the bottom right corner (plot7) you can see that it's not quite normally distributed so you may have some violations.

Cooks Distance (plot6) - used to detect outliers
https://en.wikipedia.org/wiki/Cook%27s_distance

You can see some large Cook's D values so there are likely some outliers. It would be worth investigating those observations.

Residual Quantile Plot (Plot4) - look for a straight diagonal line.
http://onlinestatbook.com/2/advanced_graphs/q-q_plots.html

You have some stragglers, so most likely those outliers.

Basically take each plot, google it and see what you should be looking for and does your data match up. If not, why.
Frequent Contributor
Posts: 108

Re: How can I access the model quality through the diagnostics panel?

 

Spoiler
 

The Link you have provided it almost tells every thing.In your case the Rsqure is is only .40 that means there are other variables which are accounted for .60 or 60%. Your Adj Rsquare is even more less 37% . Find out all those variables and do multiple regression . Your plots (No1)looks dont look like a fan shape or semicircle that which menas it is ok . You have one outlier as per the C'D panel (No 6).

Sayng so , please have a look at your data , Remove the outlier.Please understand with the theory first. I am also just learning ,but not reached Regression Analysis yet .so i could not provide much ,may be others can help.

 

Contributor
Posts: 48

Re: How can I access the model quality through the diagnostics panel?

Thanks pearsoninst, it is very nice of you.
Contributor
Posts: 48

Re: How can I access the model quality through the diagnostics panel?

Thanks Reeza, it helps.
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