Sometimes the data we need may not be available from internal or external sources. In such cases, we may have to obtain data by conducting our own survey or experiment. In a survey, we do not exercise any control over the factors when we collect information. For example, if we want to collect data on the money various families spent last month on clothes, we will ask each of the families included in the survey how much it spent last month on clothes. Then we will record this information. A survey may be a census or a sample survey. (i) Census
A census includes every member of the population of interest, which is called the target population. In practice, a census is rarely taken because it is very expensive and time consuming. Furthermore, in many cases it is impossible to identify each member of the target population. (ii) Sample Survey
Usually, to conduct research, we select a portion of the target population. This portion of the population is called a sample. Then we collect the required information from the elements included in the sample. A survey can be conducted by personal interviews, by telephone, or by mail. The personal interview technique has the advantages of a high response rate and a high quality of answers obtained. However, it is the most expensive and time-consuming technique. The telephone survey also gives a high response rate. It is less expensive and less time-consuming than personal interviews. Nonetheless, a problem with telephone surveys is that many people do not like to be called at home, and those who do not have a phone are left out of the survey. A survey conducted by mail is the least expensive method, but the response rate is usually very low. Many people included in such a survey do not return the questionnaires. Conducting a survey that gives accurate and reliable results is not an easy task.
In an experiment, we exercise control over some factors when we collect information. For example, how is a new drug to be tested to...
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