Data from: On the relationship between body condition and parasite infection in wildlife: a review and meta‐analysis

Body condition metrics are widely used to infer animal health and to
assess costs of parasite infection. Since parasites harm their hosts,
ecologists might expect negative relationships between infection and
condition in wildlife, but this assumption is challenged by studies
showing positive or null condition–infection relationships. Here, we
outline common condition metrics used by ecologists in studies of
parasitism, and consider mechanisms that cause negative, positive, and
null condition–infection relationships in wildlife systems. We then
perform a meta‐analysis of 553 condition–infection relationships from 187
peer‐reviewed studies of animal hosts, analysing observational and
experimental records separately, and noting whether authors measured
binary infection status or intensity. Our analysis finds substantial
heterogeneity in the strength and direction of condition–infection
relationships, a small, negative average effect size that is stronger in
experimental studies, and evidence for publication bias towards negative
relationships. The strongest predictors of variation in study outcomes are
host thermoregulation and the methods used to evaluate body condition. We
recommend that studies aiming to assess parasite impacts on body condition
should consider host–parasite biology, choose condition measures that can
change during the course of infection, and employ longitudinal surveys or
manipulate infection status when feasible.