Quota Sampling
Quota sampling is quite frequently used in marketing research. It involves the fixation of certain quotas, which are to be fulfilled by the interviewers
Suppose in a certain territory we want to conduct a survey of households Their total number is 2,00,000 It is required that a sample of 1 per cent, i.e. 2000 households are to be coveredWe may fix certain controls which can be either independent or inter-related These controls are shown in the following tables
A sample of 2000 households has been chosen, subject to the condition that 1200 of these should be from rural areas and 800 from the urban areas of the territory Likewise, of the 2000 households, the rich households should number 150, the middle class ones 650 and the remaining 1200 should be
Independent Controls |
|||
Rural | 1200 | Rich | 150 |
Urban | 800 | Middle class | 650 |
Poor | 1200 | ||
Total |
2000 | Total | 2000 |
Inter-related Controls |
|||
Rural | Urban | Total | |
Rich | 100 | 50 | 150 |
Middle class | 400 | 250 | 650 |
Poor | 700 | 500 | 1200 |
Total | 1200 | 800 | 2000 |
from the poor class These are independent quota controls The second table shows the inter-related quota controls As can be seen, inter-related quota controls allow less freedom of selection of the units than that available in the case of independent controls
There are certain advantages in both the schemes Independent controls are much simpler, especially from the viewpoint of interviewers They are also likely to be cheaper as interviewers may cover their quotas within a small geographical area In view of this, independent controls may affect the representativeness of the quota sampling Interrelated quota controls are more representative though such controls may involve more time and effort on the part of interviewers Also, they may be costlier than independent quota controls
In view of the non-random element of quota sampling, it has been severely criticized especially by statisticians, who consider it theoretically weak and unsound There are points both in favor of and against quota sampling These are given below
Advantages of quota sampling
(a)Â Â Â It is economical as traveling costs can be reduced An interviewer need not travel all over a town to track down pre-selected respondents However, if numerous controls are employed in a quota sample, it will become more expensive though it will have less selection bias
(b)Â Â It is administratively convenient The labor of selecting a random sample can be avoided by using quota sampling Also, the problem of non-contacts and call-backs can be dispensed with altogether
(c)Â Â Â When the field work is to be done quickly, perhaps in order to minimize memory errors, quota sampling is most appropriate and feasible
(d)Â Â It is independent of the existence of sampling frames Wherever a suitable sampling frame is not available, quota sampling is perhaps the only choice available
Limitations of Quota sampling
1 Since quota sampling is not based on random selection, it is not possible to calculate estimates of standard errors for the sample results
2 It may not be possible to get a ‘representative’ sample within the quota as the selection depends entirely on the mood and convenience of the interviewers
3 Since too much latitude is given to the interviewers, the quality of work suffers if they are not competent
4 It may be extremely difficult to supervise the control and field investigation under quota sampling
11 Comments