Figure 1

Study design (Fig. 1a) & conceptual model (Fig. 1b). Note (a). The main analyses regarding the longer-term change in friendship closeness were based on biweekly survey 3 to 9 (i.e., until the Covid-19 school lock-down). The exploratory analyses also included survey 10 to 13 to examine the impact of the lock-down on the longer-term change in friendship closeness. Note (b) R-g-r is rich-get-richer hypothesis; p-g-r is poor-get-richer hypotheses. Short-term social media-induced increases in friendship closeness are operationalized as a positive person-specific within-person effect of social media use with friends on friendship closeness. Longer-term developmental growth in friendship closeness is operationalized as a positive person-specific effect of week of study on friendship closeness.