# [R] Issue about eRM package

Tue Sep 28 11:37:09 CEST 2021

``` I am using your excellent R package eRM to solve a questionaire survey data. I meet a strange issue when using RSM function. This RSM runs well using sample data.

There is a test data like this:

'data.frame':   1669 obs. of  7 variables:

\$ X1: num  2 2 3 3 2 3 4 4 3 2 ...

\$ X2: num  4 3 3 2 3 4 4 4 3 3 ...

\$ X3: num  4 3 3 4 3 3 4 4 3 0 ...

\$ X4: num  2 3 2 4 1 2 3 3 3 1 ...

\$ X5: num  4 4 3 3 3 4 4 4 3 3 ...

\$ X6: num  4 4 4 3 3 4 4 4 3 3 ...

\$ X7: num  4 2 3 4 3 3 4 4 3 3 ...

###

RSM(test)

Warning in sqrt(diag(solve(parest\$hessian))) : NaNs produced

Warning in sqrt(diag(lres\$W %*% solve(parest\$hessian) %*% t(lres\$W))) :

NaNs produced

Results of RSM estimation:

Call:  RSM(X = test)

Conditional log-likelihood: 13768080

Number of iterations: 5

Number of parameters: 9

Item (Category) Difficulty Parameters (eta):

X2        X3       X4        X5        X6        X7     Cat 2     Cat 3       Cat 4

Estimate -700.9534 -456.4338 901.4649 -1322.033 -1256.828 -673.2412 -231.5791 -3979.953 1911.748203

Std.Err        NaN       NaN      NaN       NaN       NaN       NaN       NaN       NaN    1.036215

###

So, I use a shortened data, run like this:

RSM(test[1:283,])

Results of RSM estimation:

Call:  RSM(X = test[1:283, ])

Conditional log-likelihood: -1015.388

Number of iterations: 29

Number of parameters: 9

Item (Category) Difficulty Parameters (eta):

X2         X3        X4         X5         X6         X7     Cat 2     Cat 3    Cat 4

Estimate -0.0739008 0.05655997 1.2203061 -1.1212188 -0.7547957 -0.0378593 1.2020940 3.2657449 8.501760

Std.Err   0.1018267 0.10026033 0.1003035  0.1195827  0.1125677  0.1013739 0.4387487 0.8161754 1.226057

###

However, when I add one record, from 283 to 284,

RSM(test[1:284,])

Warning in sqrt(diag(solve(parest\$hessian))) : NaNs produced

Warning in sqrt(diag(lres\$W %*% solve(parest\$hessian) %*% t(lres\$W))) :

NaNs produced

Results of RSM estimation:

Call:  RSM(X = test[1:284, ])

Conditional log-likelihood: 3369344

Number of iterations: 6

Number of parameters: 9

Item (Category) Difficulty Parameters (eta):

X2        X3         X4        X5        X6        X7     Cat 2     Cat 3       Cat 4

Estimate -670.9137 -554.6215 527.789997 -1359.721 -1127.137 -626.1859 -126.7199 -4753.367 2134.408482

Std.Err  2152.9823 1679.2875   2.377241       NaN       NaN 3394.5180  562.6800 11045.935    3.526018

I can’t find any special values in the data list

X1 X2 X3 X4 X5 X6 X7

270  4  4  4  3  4  4  4
271  3  3  3  1  3  3  3
272  4  3  4  1  4  4  4

273  3  3  3  3  3  3  3

274  3  3  4  4  3  3  4

275  3  3  3  3  3  3  3

276  1  3  3  3  3  3  3

277  3  3  3  2  4  4  4

278  2  3  2  1  3  3  3

279  3  3  3  2  3  3  3

280  3  3  2  2  3  3  3

281  3  4  4  3  4  3  3

282  2  2  2  2  2  2  2

283  3  4  3  1  4  3  3

284  2  4  2  1  4  3  2

285  3  3  3  3  3  3  3

286  4  4  3  4  4  4  4

287  4  3  4  0  3  4  4

288  0  3  4  0  4  4  1

289  4  4  4  4  4  4  4

290  3  3  3  3  3  3  2

If I input many different numbers of data, the results often become strange.

The data is appended at the letter. No na values in all data.

Great thanks

#### all data  is in the appended file

```