In modern writing and speech (e.g., newspapers, magazines), the word data is often used with a singular verb.  However, datum is the singular form of this noun and needs a singular verb (e.g., is, was) and data is the plural form, which requires a plural verb (e.g., are, were).  Although this topic has been debated at length, the scientific community tends to prefer the stricter interpretation that data is always to be treated as a plural noun.