StabCont function

parameter stability test for continuous partitioning variable

Performs parameter stability test (Kundu and Harezlak, 2019) with continuous partitioning variable to determine whether the parameters of linear mixed effects model remains same across all distinct values of given continuous partitioning variable.

StabCont(data, patid, fixed, splitvar)

Arguments

• data: name of the dataset. It must contain variable specified for patid (indicating subject id) and all the variables specified in the formula and the StabCont(data, fixed, splitvar)partitioning variable of interest specified in splitvar.
• patid: name of the subject id variable.
• fixed: a two-sided linear formula object describing the fixed-effects part of the model, with the response on the left of a ~operator and the terms, separated by + operators, on the right. Model with -1 to the end of right side indicates no intercept. For model with no fixed effect beyond intercept, please specify only 1 right to the ~ operator.
• splitvar: the continuous partitioning variable of interest. It's value should not change over time.

Details

The continuous partitioning variable of interest. It's value should not change over time.

where $W_i(t)$ is the design matrix, theta is the parameter associated with $W_i(t)$ and b_i is the random intercept. Also, $epsilon_{it} ~ N(0,sigma ^2)$

and $b_i ~ N(0, sigma_u^2)$. Let $X$ be the baseline continuous partitioning variable of interest. StabCont() performs the following omnibus test

$H_0:theta_{(g)}=theta_0$ vs. $H_1: theta_{(g)} ^= theta_0$, for all g

where, $theta_{(g)}$ is the true value of $theta$ for subjects with $X=C_g$

where $C_g$ is the any value realized by $X$.

Returns

• p: It returns the p-value for parameter instability test

Author(s)

Madan Gopal Kundu madan_g.kundu@yahoo.com

References

Kundu, M. G., and Harezlak, J. (2019). Regression trees for longitudinal data with baseline covariates. Biostatistics & Epidemiology, 3(1):1-22.

See Also

StabCont, LongCART, plot, text

Examples

#--- Get the data
data(ACTG175)
               
#--- Run StabCont()                
out<- StabCont(data=ACTG175, patid="pidnum", fixed=cd4~time, splitvar="age")
out$pval