The number of participants needed depends on the complexity of your research question, the number of assessments over time, and the desired statistical power. Typically, Latent Growth Curve Modeling (LGCM) is used in longitudinal studies with more than two assessments over time. In such cases, data from multiple time points such as baseline and follow-up at different intervals are required.

In Cross-Lagged Panel Analysis, like LGCM, the number of participants you need depends on your study design and research question. You should have data from at least two-time points for each participant.

It is important to remember that the exact number of participants and time points in both methods will vary depending on your research context, study design, and the data you have available.