Use of the word 'Data'

Data is information, usually in the form of facts or statistics that can be analysed or used in further calculations.
Such tasks require the worker to process a large amount of data.
This will make the data easier to collect.

Data is usually regarded as an uncount noun and is used with a singular form of a verb.
The data was still being processed at the Census Office.
...whenever the data involves confrontation between nuclear powers.

People usually say this data, rather than `these data'.
Processing this data only takes a moment.
He may be incapable of transferring this data correctly to a patient's records.

However, some people think these uses are incorrect. They say that data is the plural form of the noun `datum', and should therefore be used with a plural form of a verb. They also say that you should talk about these data, not `this data'.
He now denies that all knowledge comes from the senses at the moment the sense data are received.
For the most part these data are properly handled by conventional dualistic logic.

It is probably best in any kind of formal or scientific writing to use a plural form of a verb with data and to talk about these data rather than `this data'. In other situations, you can use either form.

Source:
(c) HarperCollins Publishers.