Metrics for quantifying co-development at the individual level

Previous research on co-development has focused on modeling the relations at the group level; however, how individuals differ in co-development may provide important information as well. Recent work has used vector plots to visually explore individual differences in co-development; however, these judgements were made based on visual inspection of a vector plot rather than the calculation of metrics. Here we propose two metrics that can be used to quantify co-development at the individual level: the co-development change ratio (CCR) and the angle of co-development metric (ACM). CCR provides information about the symmetry of development, examining whether an individual grew at the same pace in one skill relative to peers as compared to growth in the other skill relative to peers. ACM represents the relative amount and direction of change on each skill. This paper provides a tutorial on how to calculate and interpret these two metrics for quantifying co-development at the individual level.