  Mobile users today interact with a variety of mobile device types including
smartphones, tablets, smartwatches, and others. However research on mobile
device type substitution has been limited in several respects including a lack
of detailed and robust analyses. Therefore, in this work we study mobile device
type substitution through analysis of multidevice usage data from a large
US-based user panel. Specifically, we use regression analysis over paired user
groups to test five device type substitution hypotheses. We find that both
tablets and PCs are partial substitutes for smartphones with tablet and PC
ownership decreasing smartphone usage by about 12.5 and 13 hours/month
respectively. Additionally, we find that tablets and PCs also prompt about 20
and 57 hours/month respectively of additional (non-substituted) usage. We also
illustrate significant inter-user diversity in substituted and additional
usage. Overall, our results can help in understanding the relative positioning
of different mobile device types and in parameterizing higher level mobile
ecosystem models.
