Which are those which have already been collected by someone is and which have already been passed through the statistical process?

Data

The facts and figures which can be numerically measured are studied in statistics. Numerical measures of the same characteristics are known as observation and collection of observations is termed as data. Data are collected by individual research workers or by organizations through sample surveys or experiments, keeping in view the objectives of the study. The data collected may be:

1. Primary Data
2. Secondary Data

Primary and Secondary Data in Statistics

The difference between primary and secondary data in Statistics is that Primary data is collected firsthand by a researcher (organization, person, authority, agency or party, etc.) through experiments, surveys, questionnaires, focus groups, conducting interviews, and taking (required) measurements, while the secondary data is readily available (collected by someone else) and is available to the public through publications, journals, and newspapers.

Primary Data

Primary data means the raw data (data without fabrication or not tailored data) which has just been collected from the source and has not gone through any kind of statistical treatment like sorting and tabulation. The term primary data may sometimes be used to refer to first-hand information.

Sources of Primary Data

The sources of primary data are primary units such as basic experimental units, individuals, households. Following methods are used to collect data from primary units usually and these methods depend on the nature of the primary unit. Published data and the data collected in the past is called secondary data.

• Personal Investigation
  The researcher conducts the experiment or survey himself/herself and collected data from it. The collected data is generally accurate and reliable. This method of collecting primary data is feasible only in case of small scale laboratory, field experiments or pilot surveys and is not practicable for large scale experiments and surveys because it take too much time.
• Through Investigators
  The trained (experienced) investigators are employed to collect the required data. In case of surveys, they contact the individuals and fill in the questionnaires after asking the required information, where a questionnaire is an inquiry form having a number of questions designed to obtain information from the respondents. This method of collecting data is usually employed by most of the organizations and its gives reasonably accurate information but it is very costly and may be time taking too.
• Through Questionnaire
  The required information (data) is obtained by sending a questionnaire (printed or soft form) to the selected individuals (respondents) (by mail) who fill in the questionnaire and return it to the investigator. This method is relatively cheap as compared to “through investigator” method but non-response rate is very high as most of the respondents don’t bother to fill in the questionnaire and send it back to investigator.
• Through Local Sources
  The local representatives or agents are asked to send requisite information who provide the information based upon their own experience. This method is quick but it gives rough estimates only.
• Through Telephone
  The information may be obtained by contacting the individuals on telephone. Its a Quick and provide accurate required information.
• Through Internet
  With the introduction of information technology, the people may be contacted through internet and the individuals may be asked to provide the pertinent information. Google survey is widely used as online method for data collection now a day. There are many paid online survey services too.

It is important to go through the primary data and locate any inconsistent observations before it is given a statistical treatment.

Secondary Data

Data that has already been collected by someone, may be sorted, tabulated, and has undergone a statistical treatment. It is fabricated or tailored data.

Sources of Secondary Data

The secondary data may be available from the following sources:

• Government Organizations
  Federal and Provincial Bureau of Statistics, Crop Reporting Service-Agriculture Department, Census and Registration Organization etc
• Semi-Government Organization
  Municipal committees, District Councils, Commercial and Financial Institutions like banks etc
• Teaching and Research Organizations
• Research Journals and Newspapers
• Internet