# Unable to provide random parameter with mlogit

I'm having trouble with rpar argument in the mlogit function (package mlogit).

My dataset looks like this:

> head(scan.s)
year id.scan day weather sealvl wave lact repro     nb.gr       HS nb.pv pup act
1 2011       1   4       2   0.30    3    1     0 0.6666667 7.600000     3   0   R
2 2011       1   4       2   0.30    3    1     0 0.6666667 7.600000     3   0   R
3 2011       1   4       2   0.30    3    1     0 0.6666667 7.600000     3   1   R
4 2011       2   4       2   0.35    3    1     0 0.6666667 8.100000     2   0   R
5 2011       2   4       2   0.35    3    1     0 0.6666667 8.100000     2   1   R
6 2011       3   4       2   0.40    3    1     0 0.6666667 8.633333     2   0   R

> str(scan.s)
'data.frame':   10140 obs. of  13 variables:
$year : int 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 ...$ id.scan: Factor w/ 280 levels "1","2","3","4",..: 1 1 1 2 2 3 3 4 4 5 ...
$day : int 4 4 4 4 4 4 4 4 4 4 ...$ weather: Factor w/ 3 levels "1","2","3": 2 2 2 2 2 2 2 2 2 2 ...
$sealvl : num 0.3 0.3 0.3 0.35 0.35 0.4 0.4 0.5 0.5 0.6 ...$ wave   : Factor w/ 4 levels "1","2","3","4": 3 3 3 3 3 3 3 3 3 3 ...
$lact : int 1 1 1 1 1 1 1 1 1 1 ...$ repro  : int  0 0 0 0 0 0 0 0 0 0 ...
$nb.gr : num 0.667 0.667 0.667 0.667 0.667 ...$ HS     : num  7.6 7.6 7.6 8.1 8.1 ...
$nb.pv : int 3 3 3 2 2 2 2 2 2 2 ...$ pup    : int  0 0 1 0 1 0 1 0 1 0 ...
$act : Factor w/ 5 levels "A","C","D","G",..: 5 5 5 5 5 5 5 5 5 5 ...  Then I used mlogit.data to transform my dataset in long shape: > scan.l<- mlogit.data(scan, varying = NULL, choice = "act", shape = "wide")  There is no variable varying across choices.  year id.scan day weather sealvl wave lact repro nb.gr HS nb.pv pup act chid alt 1.A 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 FALSE 1 A 1.C 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 FALSE 1 C 1.D 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 FALSE 1 D 1.G 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 FALSE 1 G 1.R 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 TRUE 1 R 2.A 2011 1 4 2 0.3 3 1 0 0.6666667 7.6 3 0 FALSE 2 A > str(scan.l) Classes ‘mlogit.data’ and 'data.frame': 50700 obs. of 15 variables:$ year   : int  2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 ...
$id.scan: Factor w/ 280 levels "1","2","3","4",..: 1 1 1 1 1 1 1 1 1 1 ...$ day    : int  4 4 4 4 4 4 4 4 4 4 ...
$weather: Factor w/ 3 levels "1","2","3": 2 2 2 2 2 2 2 2 2 2 ...$ sealvl : num  0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 ...
$wave : Factor w/ 4 levels "1","2","3","4": 3 3 3 3 3 3 3 3 3 3 ...$ lact   : int  1 1 1 1 1 1 1 1 1 1 ...
$repro : int 0 0 0 0 0 0 0 0 0 0 ...$ nb.gr  : num  0.667 0.667 0.667 0.667 0.667 ...
$HS : num 7.6 7.6 7.6 7.6 7.6 7.6 7.6 7.6 7.6 7.6 ...$ nb.pv  : int  3 3 3 3 3 3 3 3 3 3 ...
$pup : int 0 0 0 0 0 0 0 0 0 0 ...$ act    : logi  FALSE FALSE FALSE FALSE TRUE FALSE ...
$chid : num 1 1 1 1 1 2 2 2 2 2 ...$ alt    : chr  "A" "C" "D" "G" ...
- attr(*, "index")='data.frame':	50700 obs. of  2 variables:
..$chid: Factor w/ 10140 levels "1","2","3","4",..: 1 1 1 1 1 2 2 2 2 2 ... ..$ alt : Factor w/ 5 levels "A","C","D","G",..: 1 2 3 4 5 1 2 3 4 5 ...
- attr(*, "choice")= chr "act"


Then I ran the model:

mod1 <- mlogit(act ~ 1| nb.gr+nb.pv+sealvl+lact+repro+HS+day+id.scan,data = na.omit(scan.l), rpar=id.scan, format="long", reflevel="R", R=100, halton=NA, print.level=0)


The random parameter here is a factor and I am supposed to specify a distribution for rpar but is it relevant for a factor? (I tried to provide a distribution without any change).

And then I get this:

Error in coef(eval(callst, parent.frame())) :
error in evaluating the argument 'object' in selecting a method for function'coef' : Error in solve.default(H, g[!fixed]) : Lapack routine dgesv: system is exactly singular


There is a way to use "HS" and "day" instead, both numerical. But then I get another error:

Error in names (sup.coef) <- names.sup.coef: Attribute 'names' [1] must be the same length as the vector [0]


traceback() did not provide any insight about what happened.

I searched for explanations with those errors and found that there could be a problem between one outcome and the random effect so I tried to subset my dataset with every combination of 3 outcomes with the same result. I found nothing relevant about the second error. Maybe it has something to do with the transformation with mlogit.data. I checked the dataset provided with the mlogit package and could not figure out what I did different.

I would be grateful if someone could explain what is happening here.

Your error is because you are including the id.scan variable in the list of covariates. The error where coef() is a derivative error because the model is failing to fit correctly -- that's the second error on that same line relating to the system is exactly singular. You are confusing the rpar in this specificiation with a "grouping" variable in mixed modelling generally. rpar specifies which covariate is responding to the grouping variable. You specify the grouping variable using the argument id.var = scan.id in the call to mlogit.data().

You cannot fit a random parameter model using mlogit() for the formula you are specifying. The covariates mentioned in rpar must be alternative specific covariates -- you have to read the vignette very carefully to see that! The example provided by @John Jackson has only the alternative specific covariates (before the |) in the rpar statement. I bet if you try:

mod1 <- mlogit(act ~ 1 | nb.gr+nb.pv+sealvl+lact+repro+HS+day,data = na.omit(scan.l),  reflevel="R")


It will work fine.

I received the same error message when I tried to include a random coefficient on a person specific variable, in this case the intercept, with a wide dataset. The solution appears to be to:

1. convert the data to the long form;
2. create alternative specific intercepts by interacting a variable equal to one for all observations with each category in the alt variable;
3. estimate a model with these new variables in the list for alternative specific variables and any other person specific variables -1 after the | line;
4. specify each of the alternative specific constant terms in the npar expression.

For the Fishing example, the long data are in fish and the mlogit command is:

out<mlogit(mode~oneboat+onecharter+onepier|income-1, fish,
rpar=c(oneboat="n",onecharter="n",onepier="n"), R=100, halton=NA)


You can also do it by specifying the rpar arguments exactly as they appear when you run the regularmlogit() command. So for your example:

rpar = list("A:scan.id"="n", "C:scan.id"="n", ...)


where they named list must be quoted because of the ":" (I think, it may just be for "(", but it works with quotes either way). This is explained in footnote 20 p. 24 of Viton, PA. "Discrete-Choice Logit Models with R" (pdf):

The specification of random parameters for the alternative-specific constants has changed from mlogit version 0.1-8. The old version had rpar=c(altair='n',altbus='n',alttrain='n'). If you get an error here, try estimating model without random parameters (like model res4 above), and note how the mode-specific dummys are reported; then use that syntax in the rpar argument.

Also see the 1st paragraph of p.26 of the documentation (pdf) about having to list the entire name of individual specific coefficients. I had a similar problem when trying to just use scan.id but it stated working when I started putting the A:scan.id = argument instead. I believe you can do this with your data, as long as you set panel=F which I think is the only time the id.var=scan.id is invoked for multiple observation on the same person. If you do in fact have a panel, then don't use that variable and use the other variables you want to simulate as normal or another distribution. I'd also recommend using halton=NA argument if you have a large dataset as it speeds up the simulation significantly.

* Philip A. Viton (2014) Discrete Choice Logit Models with R. Materials for Ohio State City and Regional Planning 5700.

• Can you link to the documentation, or clarify your reference? I didn't see a footnote 20 on p 24 of the help pdf or either of the two vignettes. – gung - Reinstate Monica Oct 23 '14 at 3:30
• google.com/… – EconGeo Oct 27 '14 at 4:36
• Did you try my solution? Did it work? – EconGeo Oct 27 '14 at 4:38
• @gung did this solution work for you? – EconGeo Oct 27 '14 at 22:17
• I didn't try it. – gung - Reinstate Monica Oct 27 '14 at 22:58