The data collected may be : (A) Primary Data (B) Secondary Data (A) Primary Data : Primary data is the data which is collected by the investigator for the first time. It includes the following types: 1) Direct Personal Investigation- when researcher conducts experiment or survey and collects data himself/herself.  2) Indirect Oral Investigation- this may be done by researcher collecting data through a telephone or hiring an Investigator to do it for him/her. 3) Questionnaire Method- when required data is obtained by sending a questionnaire to selected people. This can be done by Post or sending an Ennumerator to collect the answers and record them. (B) Secondary Data :  When the investigator himself does not make any investigation, but he uses the data which has been collected by someone else, then such data is known as secondary data. He/She can get such data from published or unpublished sources. They do not have to put in much effort for data collection and thus save time, money and energy.