[R] Regarding R doubt

[shr@@k m@iii@g oii outiook@com]

library(ltm)
library(psych)

setwd("C:/Users/Admin/Desktop/IRT_CatSim")

irtdat<-read.csv("Fresh_r_2pl.csv",header=F)
head(irtdat)
PL2.rasch<-ltm(irtdat~z1)
summary(PL2.rasch)

plot(PL2.rasch,type=c("ICC"))
plot(PL2.rasch,type=c("IIC"))


Above is the code,When I run summary(PL2.rasch) I will get the following table directly:
Coefficients:
                 value           std.err   z.vals
Dffclt.V1    3.1135       9.8208  0.3170
Dffclt.V2   -0.5157       0.8941 -0.5768
�
Discrm.V1   -1.3585       3.2062 -0.4237
Discrm.V1   -1.0032    8649.3103 -0.0001
�

Working on Item response theory and I�m struggling at calculating above values manually.
You will get this difficulty and discrimination values directly, I just want the simple formulas to calculate item difficulty and item discrimination.
Also how they have calculated theta(ability) and scores at the backend of the code.


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________________________________
From: Richard O'Keefe <raoknz using gmail.com>
Sent: Thursday, June 20, 2019 2:18:26 AM
To: shraak using outlook.com
Cc: r-help using r-project.org
Subject: Re: [R] Regarding R doubt

You did not say what your doubt about R was.
PL2.rasch has some class.
> class(PL2.rasch)
[1] 'Grofnigtz'   # or whatever
The summary function is really just a dispatcher.
> summary.Grofnigtz
... a listing comes out here ...

Or you could look in the source code of whatever package you are usin.


On Thu, 20 Jun 2019 at 00:25, shraak using outlook.com<mailto:shraak using outlook.com> <shraak using outlook.com<mailto:shraak using outlook.com>> wrote:
Hello Team,
I hope you are doing well.
I have one doubt about backend functioning of R command.
Currently I'm working on IRT analysis in python but this function is implemented in R and in R they have direct rasch model library but no such library in the Python.

So I wanted to know that is there any way to find the math or formula behind the specific command of R language.
for eg, summary(PL2.rasch)
after this command you will directly get difficulty and discrimination values like mentioned below:

Coefficients:
                 value           std.err   z.vals
Dffclt.V1    3.1135       9.8208  0.3170
Dffclt.V2   -0.5157       0.8941 -0.5768
Dffclt.V3   -1.3585       3.2062 -0.4237
Dffclt.V4   -1.0032    8649.3103 -0.0001
Dffclt.V5    0.0400    1350.8452  0.0000

So is there any way to find out the math behind this summary command ?

Thanks,
Shreepad



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