On the necessity to use person-specific data analysis approaches in psychology

It is explained, both by considering earlier theoretical discussions as well as by providing analytic proof, why it is important to base analyses of developmental processes on intra-individual variation (replicated time series analysis) instead of on inter-individual variation. It is often found that replicated time series analysis yields different (person-specific) dynamic model structures across replications. A new powerful approach is presented that enables the identification of a valid common (nomothetic) dynamic model if individual replications yield person-specific dynamic model structures.