This work presents the main issues of item directionality on validity, objectivity and reliability of measurement instruments used in various fields (education, psychology or health). This is an important element to be considered in the definition of variables, the preparation of item banks, the production of tests and the interpretation of reports. Directionality depends both on the theory and the conceptual model involved in the measurement instrument, as well as the type of practice (educational or clinical for example), but it is also ruled by a “typical” behavior or response of the focal group. Item coding should not be done in terms of “presence-absence” but must take into account the direction and sense of growth of the variable as “typical-non typical”, “appropriate-non appropriate” or other distinctive unidimensional trait that should be represented in a Cartesian axis. The elements of the model of directionality are used in an instrument designed to measure the experience of the women’s symptoms with acute coronary syndrome based on the Symptom Management Conceptual Model.