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Table 3 Attributes used to assess study quality

From: A systematic review of phenotypic responses to between-population outbreeding

  Design feature Study attribute
Internal validity of study Appropriate comparator lineages used Were both parental lineages represented for each hybrid cross? 1 point for yes, 0 points otherwise
Temporal controls Were outbred and less outbred individuals studied at the same time? 1 point for yes, 0 points otherwise
Were all parental lineages observed via controlled crosses? E.g. F1 parental control cross for comparison to F1 treatment cross, F2 for F2 etc.? 1 point for yes, 0 points otherwise
Sampling strategy Were multiple independent pairs or sets of populations/lineages studied? 1 point for yes, 0 points for only a single pair of lineages
External validity of study Environment for trait observations Within what environmental context were progeny traits observed? Natural population or native habitat (1 point); environmentally realistic common garden (0.5 points); lab environment (0 points; includes glasshouses, labs, terraria, aquaria)
Observation window for inbred/outbred individuals Were phenotypic effects tracked until at least the F2 generation of progeny? 1 point for yes, 0 points otherwise
Status of populations/lineages studied Did the study include natural, naturalized, or cultivated lineages? 1 point where all populations were natural populations, 0 points where naturalized or cultivated lineages were included