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

K Imran M drki@mu@@ @ending from gm@il@com
Tue Oct 30 07:49:57 CET 2018

```Let me improve the question. On page 209, the authors wrote this for
Pr(Yij=1);
Pr(Yij=1) = 1/{1 + exp[7.31 + ....]} . Unfortunately. the values given for
the rest of the formula for Yij=2 and Yij=3.

My questions are:
1) Why v1 is 7.31 and not  -7.31
2) What are the values for v2 and v3

Thanks David for your reply. Can you be more specific?

Best wishes,

Kamarul

On Tue, Oct 30, 2018 at 1:18 PM K Imran M <drki.musa using gmail.com> wrote:

> 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)
> 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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