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
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