At the very least,reference locations from which to compute accessibilities should
exclude the places specifically visited to perform activities related
to the outcome under study. Accordingly, instead of using GPS
data that include all the places visited, it seems important to filter
GPS data based on the nature of the activities practiced at the
different places, in order to include as much daily activity places
as possible for measuring environmental exposures but without
biasing the estimated associations. For example, assuming that a
participant visits a park for exercise on the way back from his/her
workplace to his/her residence, the park would have to be
excluded from the set of locations considered to determine
greenspace accessibility, to assess whether parks are accessible
from the residence and workplace. A more technical issue is
whether the trip from the workplace to the residence with its
specific itinerary should be included as a set of locations around
which to compute greenspace accessibility