CHRNA5 and lung cancer: It is important to study change because genetic risk factors (and hence potential factors for intervention) may differ from those observed cross-sectionally in the same way that genetic risk factors for the incidence of diseases such as lung cancer (e.g., CHRNA5 as a risk factor for heaviness of smoking) may differ from genetic drivers of lung cancer progression (e.g., there is little evidence that smoking heaviness affects lung cancer survival).