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Table 1.

Features of the project's experimental design and their consequences for the independent variable (IV: nutritive value) or dependent variable (DV: butterfly visit duration).

FeatureEffect
Sucrose treatment Manipulates IV by increasing volume of available food 
Water treatment Manipulates IV by reducing concentration of naturally occurring nectar; controls for addition of colorless, odorless liquid to flower 
Unmanipulated flowers Holds IV at level equal to that of naturally occurring nectar 
Having students blind to treatment Controls for observer bias effects on DV 
Restriction of treatment to central, fully open flowers Reduces variation in DV due to flower location within inflorescence 
Random distribution of treatments across plants Reduces variation in DV due to location of inflorescence (e.g., proximity to observer) 
Random order of sampling visits to unmanipulated flowers in relation to treated flowers Reduces variation in DV due to changes across time 
Operational definition of visit duration Reduces variation in DV due to differences among observers; allows replication of study 
FeatureEffect
Sucrose treatment Manipulates IV by increasing volume of available food 
Water treatment Manipulates IV by reducing concentration of naturally occurring nectar; controls for addition of colorless, odorless liquid to flower 
Unmanipulated flowers Holds IV at level equal to that of naturally occurring nectar 
Having students blind to treatment Controls for observer bias effects on DV 
Restriction of treatment to central, fully open flowers Reduces variation in DV due to flower location within inflorescence 
Random distribution of treatments across plants Reduces variation in DV due to location of inflorescence (e.g., proximity to observer) 
Random order of sampling visits to unmanipulated flowers in relation to treated flowers Reduces variation in DV due to changes across time 
Operational definition of visit duration Reduces variation in DV due to differences among observers; allows replication of study 
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