Finally, regarding the measure of affective states, the studies included in this analysis all employed items that used unipolar response scales as opposed to a bipolar response scales. The fundamental assumption of the unipolar scale is that positive and negative affect are distinct constructs and not merely opposite ends of the same continuum (Ekkekakis, 2013). Indeed, evidence suggests that ratings of positive and negative affect are not necessarily always strongly negatively correlated in EMA research (e.g., Hyde, Conroy, Pincus, & Ram, 2011; Mermelstein, Hedeker, & Weinstein, 2010). Momentary ratings of negative affect using unipolar response scales were assessed across these EMA studies; however, due to a limited amount of intraindividua variability in negative affect, mixed-effects location scale models were unable to converge. Thus, data from these studies cannot draw conclusions about associations (or lack thereof) between subject-level variability in negative affect and overall levels of physical activity and sedentary behavior.