The short answer: data can be singular or plural. In some formal
and technical contexts the plural form is preferred, but the
singular form is increasingly common and standard. In most
contexts you can write these data or this data, data are or data
is, and so on. Data emerged in 1646 as the plural of the Latin
datum, which according to the OED was the past participle of
dare (“give”) and meant “a thing given or granted; a thing known
or assumed as a fact, and made the basis of reasoning or
calculation; a fixed starting point for a series of measurements
etc.” Datum remains standard and retains the general meaning of
“a unit of information”, though it tends to appear mostly in
academic and specialist disciplines such as philosophy,
surveying, geodesy, topography, technical drawing, and
cartography: Several map datums were erroneous, which threw the
hikers off-track. “The principal datum input to any search
algorithm is a description of its search space.” (Alan
Hutchinson, Algorithmic learning) “[T]he paper se