B. The Probability System

B. The Probability System

B. The Probability System

Using the probability system, the researcher prepares a list of the names and addresses of the entire universe which he proposes to survey. He discovers these names in city and trade directories, telephone directories or professional lists. Copies of electoral rolls, obtainable from local authorities, are also used.

Once his list is complete, the researcher sets out to select a representative sample in a uniform basis. Thus, if he intends to work with a sample of 5 per cent of the universe, he will select one name in twenty. He will not merely select 5 per cent of the list of names, because to do so would fail to ensure that the spread of names was even.

The researcher must be on his guard lest bias should enter into his sample. It has been found, for example, that people with the same initial letter to their names are not free from bias.

Since uniformity is the essence of this particular method, the interviewers employed to carry out the survey are not allowed to choose the people to be interviewed. Were they to do so, this could introduce bias because, naturally, each interviewer will be biased, to some extent, in the kind of person she selects.

There are a number of problems with the probability system of surveying, Researchers find difficulty in getting a list of all the names and addresses which make up the universe, which is not surprising. Electoral rolls and other published lists of names quickly become out of date. Also, the time spent in selecting respondents from these lists is expensive.

A further problem is that, to maintain the uniformity of the survey, a person whose name has been selected on the list must be interviewed. The pattern of uniformity will be broken if a neighbour is substituted. At first glance this may seem like pedantry carried to excess. On second thoughts, however, it will be seen that the way of life and, therefore, the buying habits of the woman who is frequently out and, therefore, difficult to get hold of, will be different from those of the woman next door who, on the contrary, is readily available simply because she is nearly always at home.

What next? - The Amount of The Advertising Appropriation

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The Trade is, of course, a major source of product ideas. All manufacturers examine, with avid interest, the new products of their competitors.