[susan53]

Postscript

I just found this in Wikipedia :

Some British and UN academic, scientific, and professional style guides (e.g., see page 43 of the World Health Organization Style Guide) request that authors treat data as a plural noun. Other international organization, such as the Institute of Electrical and Electronics Engineers Computer Society, allow its usage as either a mass noun or plural based on author preference. It is now usually treated as a singular mass noun in informal usage, but usage in scientific publications shows a strong divide between the United States and United Kingdom. In the United States the word data is often used in the singular, though scientists and science writers more often maintain the traditional plural usage. Some major newspapers such as the New York Times use it alternately in the singular or plural. In the New York Times the phrases "the survey data are still being analyzed" and "the first year for which data is available" have appeared on the same day. Scientists often use data as plural, as in These data do not support the conclusions, but most people now think of data as a singular mass entity like information and use the singular in general usage." UK usage now widely accepts treating data as singular in standard English, including everyday newspaper usage at least in non-scientific use. UK scientific publishing usually still prefers treating it as a plural. Some UK university style guides recommend using data for both singular and plural use and some recommend treating it only as a singular in connection with computers.

The original gives references to the style guides etc mentioned.