and travel) somewhat different criticisms have been raised. In a systematic review, published in 2003, of 23 randomized controlled trials, the authors found that "stage based interventions are no more effective than non-stage based interventions or no intervention in changing smoking behaviour. However, it was also mentioned that stage based interventions are often used and implemented inadequately in practice. Thus, criticism is directed towards the use rather the effectiveness of the model itself. Looking at interventions targeting smoking cessation in pregnancy found that stage-matched interventions were more effective than non-matched interventions. One reason for this was the greater intensity of stage-matched interventions. Also, the use of stage-based interventions for smoking cessation in mental illness proved to be effective. Further studies, e.g. a randomized controlled trial published in 2009, found no evidence that a TTM based smoking cessation intervention was more effective than a control intervention not tailored to stage of change. The study claims that those not wanting to change (i.e. precontemplators) tend to be responsive to neither stage nor non-stage based interventions. Since stage-based interventions tend to be more intensive they appear to be most effective at targeting contemplators and above rather than pre-contemplators. A 2010 systematic review of smoking cessation studies under the auspices of the Cochrane Collaboration found that "stage-based self-help interventions (expert systems and/or tailored materials) and individual counselling were neither more nor less effective than their non-stage-based equivalents. Main criticism is raised regarding the "arbitrary dividing lines" that are drawn between the stages. West claimed that a more coherent and distinguishable definition for the stages is needed. Especially the fact that the stages are bound to a specific time interval is perceived to be misleading. Additionally, the effectiveness of stage-based interventions differs depending on the behavior. A continuous version of the model has been proposed, where each process is first increasingly used, and then decreases in importance, as smokers make progress along some latent dimension. This proposal suggests the use of processes without reference to stages of change. West claimed that the model "assumes that individuals typically make coherent and stable plans", when in fact they often do not. However, the model does not require that all people make a plan: for example, the SAMSHA document Enhancing Motivation for Change in Substance Use Disorder Treatment, which uses the TTM, also says: "Don't assume that all clients need a structured method to develop a change plan.