Questionnaires quantify formal aspects of unidirectional communication
. This definition indicates the major limitations of research based on
such techniques: it will be unbalanced and restrictive, and therefore
incomplete. The wide use of questionnaires is often unavoidable in me
dical and scientific research, yet they are often developed with insuf
ficient attention to the needs that they are intended to meet. Their d
esign may be imperfect even in relatively straightforward circumstance
s such as the reporting of laboratory observations, but inappropriate
as well as imperfect in others, such as the study of individual qualit
y of life. This concept and others related to it are defined, together
with some major sources of error in questionnaire development and use
. Steps that can be taken to improve the situation are also mentioned.