I'm trying to run a lmer package using these codes:
summary (lmer(elabe_data$DMN_vs_DMN_z ~ elabe_data$HRLR + elabe_data$child_sex + elabe_data$mri_test_scan_day_un + elabe_data$mat_med_risk_sum + elabe_data$maternal_age_birth + elabe_data$bmi_pre_pregnancy + (1|modid), data = elabe_data))
However, I got an error message: Error: number of levels of each grouping factor must be < number of observations (problems: modid).
Does anyone know what the problem here is? I'm trying to have the identifier number (modid) as the random variable. Thanks!