Additional features are built into the design of the data collection forms to
minimize the introduction of errors into the database. For example, all categorical
responses are precoded using numeric values for data entry. Continuous
variables are recorded on preprinted fields with decimal points and measurement
units specified. In addition, shaded response boxes are used to assist the
staff in identifying when a subject does not meet eligibility criteria for a protocol
or a specific visit procedure, such as sputum induction or spirometry.