Including opt-out as alternative specific constant in R Mlogit -

i doing discrete choice experiment on preferences attributes of hypothetical drug treating weight loss in master thesis, , need little help.

my design generic, , has 12 choice sets 3 alternatives: product a, product b , option out.

somehow, need include option-out alternative specific constant, seems doing wrong here. have 197 responses on 12 choice sets of 3 alternatives, hence 197*12*3 observations of choice = 7,092

> head(choice3, 12*3) id choice_id mode.ids choice noadveff tab infreq_3 cost weightloss weightlosssq optout 1        x1             0        1  -1       -1  550        3.5        12.25     -1 1        x1        b      0       -1   1        1   90        6.0        36.00     -1 1        x1        c      1        0   0        0    0        0.0         0.00      1 1       x10             0        1  -1        1   50        6.0        36.00     -1 1       x10        b      0       -1   1       -1  165        3.5        12.25     -1 1       x10        c      1        0   0        0    0        0.0         0.00      1 1       x11             0       -1  -1        1  165        2.0         4.00     -1 1       x11        b      1        1   1       -1   90        3.5        12.25     -1 1       x11        c      0        0   0        0    0        0.0         0.00     -1 1       x12             0       -1  -1        1  550        6.0        36.00     -1 1       x12        b      0        1   1       -1 1000        2.0         4.00     -1 1       x12        c      1        0   0        0    0        0.0         0.00      1 1       x13             0       -1  -1       -1   90        6.0        36.00     -1 1       x13        b      0        1   1        1 1000        6.0        36.00     -1 1       x13        c      1        0   0        0    0        0.0         0.00      1 1        x2             0       -1  -1       -1 1000        6.0        36.00     -1 1        x2        b      0        1   1        1  300        2.0         4.00     -1 1        x2        c      1        0   0        0    0        0.0         0.00      1 1        x3             0       -1  -1        1 1000        6.0        36.00     -1 1        x3        b      1        1   1       -1   50        6.0        36.00     -1 1        x3        c      0        0   0        0    0        0.0         0.00     -1 1        x4             0        1  -1        1  165        3.5        12.25     -1 1        x4        b      0       -1   1       -1  550        2.0         4.00     -1 1        x4        c      1        0   0        0    0        0.0         0.00      1 1        x5             0       -1  -1       -1  550        2.0         4.00     -1 1        x5        b      1        1   1        1   50        6.0        36.00     -1 1        x5        c      0        0   0        0    0        0.0         0.00     -1 1        x6             0        1  -1       -1  300        6.0        36.00     -1 1        x6        b      0       -1   1        1   50        3.5        12.25     -1 1        x6        c      1        0   0        0    0        0.0         0.00      1 1        x8             0       -1  -1        1  300        3.5        12.25     -1 1        x8        b      1        1   1       -1  165        6.0        36.00     -1 1        x8        c      0        0   0        0    0        0.0         0.00     -1 1        x9             0       -1   1       -1  300        6.0        36.00     -1 1        x9        b      0        1  -1        1   90        2.0         4.00     -1 1        x9        c      1        0   0        0    0        0.0         0.00      1 

i using effects coding categorical variables (noadfeff, tab, infreq_3 , optout)

mode.ids indicate alternatives, i.e. product or b, or option-out (mode.ids == c)

the optout-variable has been coded following command,

choice2$optout <- ifelse(choice2$mode.ids == "c" & choice2$choice == 1, "1", "-1") 

using data-set set data mlogit-package

mlogit.all <- mlogit.data(choice2,             choice = "choice",             shape = c("long"),             id.var = "id",             alt.var = "mode.ids",             varying = c("cost", "cost.square", "noadvef", "tab", "infreq_3", "weightloss", "optout", "costsq", "weightlosssq"), ) 

and run following model

model.all <- mlogit(formula = choice ~ noadveff + tab + infreq_3 + cost + weightloss | optout | 0 ,                      data = mlogit.all,                      rpar = c(noadveff = 'n', tab = 'n', infreq_3 = 'n', weightloss = 'n', optout = 'u'),                      r = 100,                      halton = na,                      print.level = 0,                      panel = true ) 

which results in following error.

error in solve.default(h, g[!fixed]) :  lapack routine dgesv: system singular: u[8,8] = 0 

the similar model without optout, not give problems, must doing wrong optout-variable.

i hope can see issue is? :)

best, henrik

sorry, found error myself - solution provided beneath,

choice2$optout <- ifelse(choice2$mode.ids == "c", "1", "-1") 

hence, have asc equal 1 each alternative called c (i.e. option out)

model.all <- mlogit(formula = choice ~ noadveff + tab + infreq_3 + cost + weightloss + optout | -1 | 0 ,                      data = mlogit.all,                      rpar = c(noadveff = 'n', tab = 'n', infreq_3 = 'n', weightloss = 'n'),                      r = 100,                      halton = na,                      print.level = 0,                      panel = true ) 

after model work, , generate asc option-out'ers.