Originally Posted by
Polaris OBark
The collection of data (aka a data set) is a singular entity, because "collection" is a singular, and "set" is a singular.
"The set are complete" sounds wrong. "The set is complete" or "the data-set is complete" sounds correct.
A collection of data, sometimes termed a dataset is singular, but there can be multiple datasets. And when we refer to an accumulation of different sets of data from a number of studies, we say "the data say", not "the dataset says".