1. Direct personal observation; In this method the investigator, collects the required information by personal observation of the units, through the enumerator, from the informants. This methods is successively employed Where the field of enquiry is confidential, small, greater accuracy and sufficient time is available.

Merits: This method is most reliable, accurate and confidential. 

Demerits: This method is expensive, time consuming and this method becomes difficult where the enquiry is field of large. In this method there is chance of personal bias in collection of data, needs trained and skilled personnel.

2. Indirect oral interview: This method is applied, where the required information from the informant is not possible to obtain by direct interview method. In this method the investigator/enumerator approaches the witnesses or third parties, who are capable to supply the necessary information about the first person/informant.

Merits: This method is simple, convenient, free from bias and successively employed by News paper, Broadcasting, Investigating agencies. 

Demerits: In this method there is an ample scope of bias by influencing the enquiry by the third person.