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NKormanik
Barite | Level 11

In various SAS procedures one can generate measures of how well a model may fit -- the amount of variance that is explained by the independent variables on the target variable.

 

Example:  The HPREDUCE Procedure 

 

I'm wondering if there is a rule of thumb one aims for as far as, say, 'Proportion of Variance Explained.'  Or, AIC, AICC, BIC, etc.  While SAS provides these measures, SAS does not tell you if these are high or low enough to create a reasonable model.

 

What procedure would you use to most directly tell whether your model meets various customary standards?  What levels do you aim for?

 

Any thoughts or clarifications greatly appreciated.

 

Nicholas Kormanik

 

 

 

6 REPLIES 6
Ksharp
Super User

It is called Goodness Of Fit problem.

@Rick_SAS  have already discuss this kind of problem. You need split the predicted value of Y into several groups and using Chisquare Test.

These blog would help you a lot .

 

https://blogs.sas.com/content/iml/2018/05/16/decile-calibration-plots-sas.html

 

https://blogs.sas.com/content/iml/2018/05/14/calibration-plots-in-sas.html

 

https://blogs.sas.com/content/iml/2016/11/28/goodness-of-fit-large-small-samples.html

NKormanik
Barite | Level 11

@Ksharp as usual, terrific person.  Love the guy.

 

Just a quick post for now.  The implication of your response seems to be that The HPREDUCE Procedure has limited value and one ought to use some other better procedure??

 

Would like to know what SAS developer, Zheng Zhao , might say about that??

 

On Google images there are lots of pics of Enterprise Miner with HPREDUCE connected right after the data input, before anything else.

 

PaigeMiller
Diamond | Level 26

I haven't used HPREDUCE, but the idea of variable selection is a common thing to do, and I don't know why anyone would be skeptical of the procedure a priori. You still have to be smart about it, and select either "supervised" or "unsupervised" in HPREDUCE as your needs require.

 

There are plenty of other methods to do variable selection as well. I would advise against blindly accepting the results of any method and using human judgment to help you decide (for example, if you expect a variable to have a positive slope and the model fit produces a negative slope), no matter what method you choose.

--
Paige Miller
Rick_SAS
SAS Super FREQ

The AIC, AICC, BIC, etc are statistics that are only meaningful when you compare two different models that use the same data. By themselves, you cannot say "this statistic is high enough to believe the model." But if you fit two models, you can use them to say that one model fits the data better, with adjustments made for the complexity of the models.

 

For linear regression models, the "null model" is the intercept-only model, so you can find the "baseline" AIC (etc) by using

MODEL Y = ;  /* intercept only */

 

For logistic-type models, the ROC curve is a measurement that compares the fit to a random prediction model.

fierceanalytics
Obsidian | Level 7

Hello, 

 

Part of potential answer to your question transcends domains, model types... with binary target. For example, "percent of variance explained" typically should be over 80% or 75% at least, regardless. But be careful not to engage too many variables because if you add many enough, you can always get over 80%. 

 

One aspect of answer to your question is intrinsic, technical, inside the model mechanics, such of goodness of fit. When a model is mainly towards predicting, like digital stream response, or traditional camp response, we do not check this kind of fitness much. Instead, AUC, ROC,..... dominates while the model does often need to watch out model drivers. In traditional models like regression where your original question touches on, BIC, AIC, models often, out of domain requirement or not, do watch our model specification. With machine learning models, BIC, AIC... are often considered as secondary, defensive measure, not as primary criteria since it is practically hard to link them to popular accuracy. Still, domain matters as far as your question is concerned. If the model is 'pure prospect' targeting model, you should be happy with fairly low, weaker measures, while if the model is 'behavioral', the yardstick is much higher. Lastly, in high power DNN like models, BIC, AIC may not be part of the performance foundation at all. In the case of SVM, you don't normally get a score output. In some DNN models where all the events are captured in top, say, 1%, in other words very accurate, then there is little meaning to measure anything because you don't have traditional depth to calculate those 'old' measurement. + before running HPREDUCE, you may need to check correlation. Jia

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