help for mlmjn

Title

mlmjn -- Johnson-Neyman interval for a two-way MLM interaction

Syntax

mlmjn , pred(string) modx(string)
[options]

pred(string) focal predictor name

modx(string) moderator name

alpha(#) significance level; default 0.05

plot draw a Johnson-Neyman plot

grid(#) number of grid points for plot; default 200

saving(filename) save plot to file

Description

mlmjn computes the Johnson-Neyman (JN) interval: the value(s) of
modx at which the simple slope of pred transitions between
statistical significance and non-significance.

The boundary is computed analytically via the quadratic formula (exact
solution, not a grid search). Results are reported for boundaries that
fall within the observed range of modx.

mlmjn must be run immediately after mixed. The model must
include the interaction as c.pred##c.modx.

Stored results

r(jn1) first JN boundary (. if none in observed range)

r(jn2) second JN boundary (. if none)

r(t_crit) critical t-value used

r(df_r) residual degrees of freedom

r(b_pred) coefficient on focal predictor

r(b_int) coefficient on interaction term

Example

. mixed math c.ses_c##c.climate_c gender || school:, reml

. mlmjn, pred(ses_c) modx(climate_c)

. mlmjn, pred(ses_c) modx(climate_c) plot

. mlmjn, pred(ses_c) modx(climate_c) alpha(0.01) plot

Author

Subir Hait, Michigan State University.

Reference

Johnson, P. O., and Neyman, J. (1936). Tests of certain linear hypotheses
and their application to some educational problems.
Statistical Research Memoirs, 1, 57-93.

Also see

mlmprobe, mlmplot, mlmsummary, mlmcenter