Most of the surveys are sample surveys. These are preferred in statistics because of a number of reasons. A sample can provide reasonably, reliable and accurate information at a lower cost and shorter timeSamples are smaller than population, more detailed information can be collected by conducting intensive enquiries. As we need a smaller team of enumerators it is easier to train them and supervise their work more effectively.

Data is a tool which helps in reaching a sound conclusion on any problem by providing information.

Economic facts expressed in terms of numbers are called data. The purpose of data collection is to understand, explain and analyse a problem and causes behind it. Primary data is obtained by conducting a survey. There are other agencies which collect, process, tabulate and publish statistical data. These can be used as secondary data.

The purpose of the sample is to take an estimate of the population. Sampling error refers to the differences between the sample estimate and the actual value of a characteristic of the population. It is the error that occurs when you make an observation from the sample taken from the population.

The difference between the actual value of a parameter of the population and its estimate is the sampling error.

Non-sampling errors are more serious than sampling errors because a sampling error can be minimised by taking a larger sample. It is difficult to minimise non-sampling error, even by taking a large sample. This type of error arises from recording of incorrect response.

The National Sample Survey Organisation was established by the government of India to conduct nation-wide surveys on socioeconomic issues. The data collected by NSSO surveys on different socio-economic subjects are released through reports and its quarterly journal Sarvekshana. NSSO provides periodic estimates of literacy, school enrolment, utilisation of educational services, employment, unemployment, manufacturing and service sector enterprises, morbidity, maternity, child care, utilisation of the public distribution system etc. The NSSO also undertakes the fieldwork of annual surveys of industries, conducts crop estimation surveys, collects rural and urban retail prices for compliation of consumer price index numbers. ,

While preparing the questionnaire following points should keep in mind :

1. The questionnaire should not be too long. The number of questions should be as minimum as possible.

2. The series of questions should move from general to specific. This helps the respondents feel comfortable.

3. The questions should not be complex. The respondents can answer quickly, correctly and clearly.

4. The questions should not use double negatives. The questions starting with 'wouldn't you' or 'don't you' should be avoided.

5. The question should not be a leading question which gives a clue about how the respondent should answer.

6. The question should not indicate alternatives to the answer.