Unstructured data, which are not as easy to search or process as they do not follow a predefined structure.

Veracity of big data is not the biases, noises and inconsistencies within the data.

Secondary data offer you potential access to a far wider variety of data from a far larger sample over a longer time period than you could ever collect yourself.

Censuses are usually carried out by researchers.

Raw data that have already been selected or summarised.

Multiple source is not one form of secondary data, compiled to create a snapshot, longitudinal data or being continually updated.

Data cannot be compiled for the same population over time using a series of ‘snap- shots’ to form cohort studies.

Variety of big data is the multiplicity of unstructured and structured data being added.

Some secondary data, in particular documents such as company minutes, are available only from the organisations that sell them and so access will not need to be negotiated.

Service companies, for example, need to be included from your data if you are concerned only with manufacturing companies.