[R] Request for functions to calculate correlated factors influencing an outcome.
Prashant Sethi
theseth.prashant at gmail.com
Mon May 4 11:28:53 CEST 2015
Hi,
>From my understanding of a model, you need to have one or more dependent
parameter variables which you (y1, y2 etc) and the explanatory parameter
variables (x1, x2 etc) which you fit along with certain coefficients to
determine the dependent parameter with minimum error as possible. I don't
think a factor can be on both sides of the model equation.
In your earlier email you had mentioned this statement: Question is : I am
trying to find factors influencing efficiency (in this
case mileage)
If this is indeed your question, then I believe the lm() function is what
you need. Otherwise, I think you need to reformulate your query to further
clarify what you are looking for.
Thanks and regards,
Prashant
On Mon, May 4, 2015 at 2:10 PM, Lalitha Viswanathan <
lalitha.viswanathan79 at gmail.com> wrote:
> Hi
> I used the MASS library
> library(MASS) (by reading about examples at
> http://www.statmethods.net/stats/regression.html
> <
> http://s.bl-1.com/h/ofLlK27?url=http://www.statmethods.net/stats/regression.html
> >
> )
> fit <- lm(Mileage~Disp+HP+Weight+Reliability,data=newx)
> step <- stepAIC(fit, direction="both")
> step$anova # display results
>
> It showed the most relevant variables affecting Mileage.
> While that is a start, I am looking for a model that fits the entire data
> (including Mileage), not factors that influence Mileage.
>
> Multi model inference / selection.
>
> I was reading about glmulti.
> Are there any other packages I could look at, for infering models that best
> fit the data.
>
> To use nlm / nls, I need a formula, as one of the parameters to best fit
> the data and I am looking for functions that will help infer that formula
> from the data.
>
> Thanks
> lalitha
>
> On Sun, May 3, 2015 at 11:33 PM, Prashant Sethi <
> theseth.prashant at gmail.com>
> wrote:
>
> > Hi,
> >
> > I'm not an expert in data analysis (a beginner still learning tricks of
> > the trade) but I believe in your case since you're trying to determine
> the
> > correlation of a dependent variable with a number of factor variables,
> you
> > should try doing the regression analysis of your model. The function
> you'll
> > use for that is the lm() function. You can use the forward building or
> the
> > backward elimination method to build your model with the most critical
> > factors included.
> >
> > Maybe you can give it a try.
> >
> > Thanks and regards,
> > Prashant Sethi
> > On 3 May 2015 23:18, "Lalitha Viswanathan" <
> > lalitha.viswanathan79 at gmail.com> wrote:
> >
> >> Hi
> >> I am sorry, I saved the file removing the dot after the Disp (as I was
> >> going wrong on a read.delim which threw an error about !header,
> etc...The
> >> dot was not the culprit, but I continued to leave it out.
> >> Let me paste the full code here.
> >> x<-read.table("/Users/Documents/StatsTest/fuelEfficiency.txt",
> >> header=TRUE,
> >> sep="\t")
> >> x<-data.frame(x)
> >> for (i in unique(x$Country)) { print (i); y <- subset(x, x$Country ==
> i);
> >> print(y); }
> >> newx <- subset (x, select = c(Price, Reliability, Mileage, Weight, Disp,
> >> HP))
> >> cor(newx, method="pearson")
> >> my.cor <-cor.test(newx$Weight, newx$Price, method="spearman")
> >> my.cor <-cor.test(newx$Weight, newx$HP, method="spearman")
> >> my.cor <-cor.test(newx$Disp, newx$HP, method="spearman")
> >> Putting exact=NULL still doesn't remove the warning
> >> my.cor <-cor.test(newx$Disp, newx$HP, method="kendall", exact=NULL)
> >> I tried to find the correlation coeff for a various combination of
> >> variables, but am unable to interpet the results. (Results pasted below
> in
> >> an earlier post)
> >>
> >> Followed it up with a normality test
> >> shapiro.test(newx$Disp)
> >> shapiro.test(newx$HP)
> >>
> >> Then decided to do a kruskal.test(newx)
> >> with the result
> >> Kruskal-Wallis chi-squared = 328.94, df = 5, p-value < 2.2e-16
> >>
> >> Question is : I am trying to find factors influencing efficiency (in
> this
> >> case mileage)
> >>
> >> What are the range of functions / examples I should be looking at, to
> find
> >> a factor or combination of factors influencing efficiency?
> >>
> >> Any pointers will be helpful
> >>
> >> Thanks
> >> Lalitha
> >>
> >> On Sun, May 3, 2015 at 2:49 PM, Lalitha Viswanathan <
> >> lalitha.viswanathan79 at gmail.com> wrote:
> >>
> >> > Hi
> >> > I have a dataset of the type attached.
> >> > Here's my code thus far.
> >> > dataset <-data.frame(read.delim("data", sep="\t", header=TRUE));
> >> > newData<-subset(dataset, select = c(Price, Reliability, Mileage,
> Weight,
> >> > Disp, HP));
> >> > cor(newData, method="pearson");
> >> > Results are
> >> > Price Reliability Mileage Weight Disp
> >> > HP
> >> > Price 1.0000000 NA -0.6537541 0.7017999 0.4856769
> >> > 0.6536433
> >> > Reliability NA 1 NA NA NA
> >> > NA
> >> > Mileage -0.6537541 NA 1.0000000 -0.8478541 -0.6931928
> >> > -0.6667146
> >> > Weight 0.7017999 NA -0.8478541 1.0000000 0.8032804
> >> > 0.7629322
> >> > Disp 0.4856769 NA -0.6931928 0.8032804 1.0000000
> >> > 0.8181881
> >> > HP 0.6536433 NA -0.6667146 0.7629322 0.8181881
> >> > 1.0000000
> >> >
> >> > It appears that Wt and Price, Wt and Disp, Wt and HP, Disp and HP, HP
> >> and
> >> > Price are strongly correlated.
> >> > To find the statistical significance,
> >> > I am trying sample.correln<-cor.test(newData$Disp, newData$HP,
> >> > method="kendall", exact=NULL)
> >> > Kendall's rank correlation tau
> >> >
> >> > data: newx$Disp and newx$HP
> >> > z = 7.2192, p-value = 5.229e-13
> >> > alternative hypothesis: true tau is not equal to 0
> >> > sample estimates:
> >> > tau
> >> > 0.6563871
> >> >
> >> > If I try the same with
> >> > sample.correln<-cor.test(newData$Disp, newData$HP, method="pearson",
> >> > exact=NULL)
> >> > I get Warning message:
> >> > In cor.test.default(newx$Disp, newx$HP, method = "spearman", exact =
> >> NULL)
> >> > :
> >> > Cannot compute exact p-value with ties
> >> > > sample.correln
> >> >
> >> > Spearman's rank correlation rho
> >> >
> >> > data: newx$Disp and newx$HP
> >> > S = 5716.8, p-value < 2.2e-16
> >> > alternative hypothesis: true rho is not equal to 0
> >> > sample estimates:
> >> > rho
> >> > 0.8411566
> >> >
> >> > I am not sure how to interpret these values.
> >> > Basically, I am trying to figure out which combination of factors
> >> > influences efficiency.
> >> >
> >> > Thanks
> >> > Lalitha
> >> >
> >>
> >> [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
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> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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