Big data can therefore be thought typically as can be drawn from a wide variety of online sources, public records.

Many small organisations also undertake regular surveys.

Validity of big data is not whether the data are correct.

obtrusive is one advantage of secondary data.

Censuses are not clearly defined.

Primary data is data that have already been collected for some other purposes.

For all secondary data sets coverage will be concerned with ensuring that unwanted data are or can be included.

Permanence of data is one advantage of secondary data.

Secondary data exclude qualitative (non-numeric) data.

Big data have the enormous size of the data set due to the aggregation of large numbers of variables and the even larger number of observations.