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Questionnaires have long been used by medical epidemiologists as a means of collecting data from individuals on exposure to risk factors. They are now being increasingly used by veterinary epidemiologists and researchers in other disciplines such as forestry and wildlife biology. In some areas the increasing use reflects greater interest in obtaining the views of the public, for example perceptions or attitudes towards conservation strategies. In other areas it reflects the rising cost of field research and the (often mistaken) belief that one can get reliable information just by sending round a questionnaire rather than going to the field oneself.
Sample selection for a questionnaire is covered
Questionnaire constructionThere are three basic type of questions that can be asked.
(a) The first type is the closed question where the answer is either binary, multiple choice, or requires some sort of rating on a scale. If multiple choice categories are given they should be mutually exclusive (categories should not overlap) and exhaustive (covering all possible answers). The latter often requires a dumping category such as 'others', or 'don't know'. Avoid an excessively large number of categories (more than ten) and try to minimize the number of responses in the dumping category.
(b) The second type is the open question where the respondent can answer in his or her own words. Closed questions are both quicker and easier to answer and to analyse, but they can unnecessarily constrain responses on some issues.
(c) A third approach is to set a discussion topic which is then put to a focus group (see
Questions should be clear and concise and each should focus on one issue. Vague adjectives such as 'many' and 'occasionally' should be avoided - use specific terms instead such as 'more than 20' or 'less than once a week'. Related questions should be grouped together so that it is easier for the respondent to follow. Keep the questionnaire as short as possible to adequately cover the topic - however large the topic it is very unwise to exceed 30 minutes per respondent as the response rate will fall and measurement error will increase.
If possible the questionnaire should be developed in the language of the respondent group. If translation is necessary, then the translated version should be always back-translated by someone blinded to the original questionnaire, and the result compared with the original.
Any questionnaire should be piloted with a small random sample of the population to test how well it performs in terms of comprehension and time for completion. A questionnaire should only be implemented after it has gone through this test.
Methods of implementationThere are several methods of implementing a questionnaire:
(a) A postal survey self-completed by the respondent is still the most common method used for large scale surveys. It has the advantages of low cost, and elimination of interviewer bias (see
(b) Telephone interviews have been increasingly used in recent years. They retain most of the advantages of in-person interviews and are much cheaper to implement - but carry with them a high risk of selection bias if not everyone is on the phone, or equally willing to be interviewed that way (see
(c) In-person interviews are the method of choice where it is felt that the presence of an interviewer will make the questionnaire more comprehensible or increase the response rate. They are sometimes the only method that can be used in areas where telecommunications services are not well developed.
(d) In all the above methods the sampling unit is the individual. If one wishes to investigate motivations or perceptions it may be more appropriate to use the focus group approach. Here a topic / questionnaire is discussed by a small groups of respondents. Ideally the individuals in the groups would be randomly selected, but commonly they are purposively selected either to be 'representative' of the community, or to specifically include key opinion leaders.
Sources of error and biasHigh levels of error and bias are commonly associated with information obtained by questionnaire: