This study is limited due to lack of a randomly assigned control group and lack of comparison between the RLH and TI - TAU group on most outcome measures, and possible selection bias in the RLH sample. (cebc4cw.org)
The researchers noted possible selection bias, as a number of participants contacted for the study did not complete initial surveys and link Cardiogram accounts. (ucsf.edu)
Limitations include possible selection bias as no information is provided on the Parents Anonymous ® members who refused to participate in the study, the lack of a control group, and threats to internal validity (cebc4cw.org)