Multiplicity fraction of Class II and III stars observed at HAR and members of UWPs as a function of their separation. For a given value of δ, the black (resp. blue) symbol represents the multiplicity fraction computed over all separations smaller (resp. greater) than δ. Errorbars are standard errors computed from the standard formula: where n_i is the sample size, and N is the total population size of Class II and III stars observed at HAR within UWPs independently of their separation. The dashed black line represents the mean multiplicity fraction for stars within UWPs whereas the gray line marks the corresponding mean multiplicity fraction for stars that are not in UWPs. The red dotted lines define the interval within which the multiplicity fraction within UWPs is significantly (p-value of 0.05 or less based on a chi-squared test) higher than the mean value.