[R-sig-ME] intercept and threshold values to calculate probability based on mixor package

[K Imran M]

Hi everyone,

I need help to identify the values for intercept and thresholds in the
equations to calculate the probability (based on cumulative link models).

On page 209 in Longitudinal Data Analysis book by Hedeker, the
probabilities are written as:

Pr(Yij=1) = 1/{1 + exp[-(v1 -(xijB+zijV))]}
Pr(Yij=2) = 1/{1 + exp[-(v2 -(xijB+zijV))]} - Pr(Yij=1)
Pr(Yij=3) = 1/{1 + exp[-(v3 -(xijB+zijV))]} - Pr(Yij=2)
Pr(Yij=4) = 1 - 1/{1 + exp[-(v3 -(xijB+zijV))]}

My question is what are the values for v1, v2 and v3?

The R scripts below shows the codes and the results from running mixor.

library(mixor)
#> Loading required package: survival
data("schizophrenia")
mixor.mod <- mixor(imps79o ~ TxDrug + SqrtWeek + TxSWeek,
                     data = schizophrenia, id = id, which.random.slope = 2,
link = "logit")
summary(mixor.mod)

#>
#>                          Estimate Std. Error z value   P(>|z|)
#> (Intercept)              7.318831   0.480778 15.2229 < 2.2e-16 ***
#> SqrtWeek                -0.882261   0.234568 -3.7612 0.0001691 ***
#> TxDrug                   0.057917   0.399102  0.1451 0.8846178
#> TxSWeek                 -1.694861   0.268131 -6.3210 2.598e-10 ***
#> (Intercept) (Intercept)  6.997646   1.369273  5.1105 3.213e-07 ***
#> (Intercept) SqrtWeek    -1.508514   0.536023 -2.8143 0.0048888 **
#> SqrtWeek SqrtWeek        2.008916   0.453587  4.4290 9.469e-06 ***
#> Threshold2               3.901260   0.213257 18.2937 < 2.2e-16 ***
#> Threshold3               6.507172   0.289991 22.4392 < 2.2e-16 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1


Thank you very much.

Best wishes,

Kamarul Imran Musa
MD PhD
Universiti Sains Malaysia
Malaysia

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