Types of Data

The first step of any statistical enquiry is the collection of relevant numerical data. The types of data used for statistical purposes is mainly classified as primary data and secondary data

Variable

a characteristic of population that can take different values (e.g., defects, processing time).

Data

Data are measurements collected on a variable

Primary Data

Data collected for the purpose of the given inquiry is called as Primary Data. These are collected by the enquirer, either by his own or through some agency set up for this purpose, directly from the field of enquiry. This type of data can be used with greater confidence because the enquirer himself decides upon the coverage of the data, definitions to be used and as such will have a greater control over the reliability of the data.

Secondary Data

The data already collected by some other agency or for some other purpose and available in published or un published form is known as secondary data. The user has to be perticularly careful about using using such data. The user must clearly understand the nature of the data, their coverage, the definitions used for the data and their reliability.
The usage of secondary data is generally preferred if the conditions mentioned above are clear and usable. This will reduce the time taken for the analysis, also reduces cost of the analysis.

Discrete Data

Count or frequency of occurrence

Attribute Data

Data which on one of a set of discrete values such as pass or fail, yes or no.

Continuous Data

Measurements that can be meaningfully divided into finer and finer increments of precision

Usage of Sampling

The big question is weather the collection of data should be done by complete population or by sampling. If sample is used, care should be taken that this is a representative of complete population. A sample designed with care can produce results that may be sufficiently accurate for the purpose of enquiry. A Carefully designed sample can save a lot of time and money.

Methods of Data Collection

The methods used to collect data are Questionnaire Method, Interview Method and Direct Observation Method. Any one or a combination of these are used to collect data.

Usage of Data

The data collected should be subjected to a thorough scrutiny to see if they may be considered correct. The success of the analysis depends on the reliability of the data. However excellent the statistical method of data analysis may be, they cannot bring out useful and reliable information from faulty, unreliable of mistaken data. Especially, this is more applicable in case of usage of secondery data.

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