I refer to the item that appeared in the On the Dot column titled ‘Mystery caller’ (April 23) about the telephone surveys carried out by the National Statistics Office.

When conducting telephone surveys, the NSO applies the so-called ‘sampling quotas’, whereby individuals are selected at random subject to specific socio-demographic characteristics (including, but not limited to, sex, age group and district of residence).

For this reason, although the NSO originally selects a sufficiently large sample that guarantees an adequate overall allotment, once the desired number of responses is reached in all categories, interviews are stopped and, thus, part of the sample will always remain unutilised.

Given that interviewees are selected randomly, the NSO has no means of identifying them beforehand and that explains why it is not advisable to mail out an explanatory letter prior to the survey to inform all individuals.

Although, technically speaking, it is possible to send a letter to all eligible participants, since some of these will not be required to participate in the survey (for the reasons outlined above), in addition to being operationally unfeasible, this could also lead to additional confusion among the public.

Should any member of the public require further information, s/he is encouraged to contact our offices on 2599 7219 between 8am and 3.45pm.