Measuring progress toward smoking cessation.

Measuring the effect of behavioral interventions is often limited to a single outcome variable for ease of analysis. In the case of low probability outcomes, this narrow focus may often result in Type II errors, reducing the likelihood of detecting an effect of an intervention. The development and use of a scale to measure progress toward the ultimate desired change in behavior might result in greater sensitivity to subtle, but important, effects of interventions. That possibility is illustrated by the development and exploratory testing of a scale meant to measure penetration into the process of change with respect to smoking cessation. The scale consists of a set of outcome indicators that are intended to represent the sequential steps that smokers go through in moving toward and ultimately giving up smoking. Rasch analyses indicate that the scale is coherent and merits further development. It seems likely that similar scales might be developed to assess progress toward change for many other behaviors that seem to require a gradual process of change that can be indexed by items representing discrete steps along the way.