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 field is 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 New paper, Broadcasting, Investigating agencies. 

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

3. Information through agencies 

Under this method, local agents or correspondents will be appointed. They collect the information and transmit it to the investigator. They may apply any method according to the intensity of the situation. Agents who collect information from the informants are generally called correspondents.

This method is generally adopted in those cases where the information is to be obtained at regular intervals from a wide area. News papers are the-examples of collection of information through agencies.

Merits : 

• This method is very cheap and economical. 
• It is useful where information is needed regularly. 

Demerits:

• The information may be biased. 
• It is difficult to maintain the degree of accuracy and uniformity.

4. Mailed questionnaire 

Questionnaire is a list of questions where the answers are filled by the informants and these answers are the required information for the investigation. The questionnaire is sent to the respondents, who are expected to write the answers in the space provided in the questionnaire.

The questionnaire will by sent to the informants through mail. A covering letter is also sent along with the questionnaire, requesting the informants to extend their full cooperation by giving the correct information and return the duly filled questionnaire with in a fixed time. This method is appropriate in cases where informants are spread over a wide area and are literates.

Merits: 

• This method is most economical. 
• It saves manpower. 
• It can be widely used, where the area of investigation is large. 

Demerits: 

• This method cannot be used if the informants are illiterates. 
• In this method many informants will not respond. 
• In the case of non response, follow up work is essential.

5. Schedules sent through enumerators: It is a widely used method of collection of primary data. A number of enumerators are selected and trained for this purpose.

Here, the trained investigator collects data through enumerators. The enumerators contact the informants and collect the information which is called schedule method. Schedule is a list of questions where the facts will be supplied by informants and recorded by enumerator.

Merits 

• This method is very useful where the informants are illiterates. 
• In this method the rate of non response is less. 

Demerits 

• In this method the training of enumerators is essential. 
• This method is time consuming. 
• Personal bias of the enumerators may lead to failure of enquiry.