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  • The study sample comprised of 183 participants, of which 114 were patients and 69 were healthy comparisons. Written ethics approval was obtained from the Sydney Local Health District human research ethics committee. (Approval number: X16-0356). Participants provided their written informed consent before participating in the study. This consent procedure was approved by the committee. Patients were being treated for heroin addiction by opioid medication (methadone or buprenorphine) at the Drug Health Services and Opioid Treatment Program at the Royal Prince Alfred Hospital in Sydney, Australia. Opioid dependence was confirmed by DSM-IV criteria and urinalysis. The comparison group participants were recruited from psychology students at Western Sydney University and from the wider western Sydney community, through snowballing and advertisements. History of opioid use was an exclusion criterion for the comparison group as assessed by a drug screening questionnaire. All participants completed a demographic questionnaire assessing age, gender, years of education, and efforts were made to match control participants with patients on these variables. Patients also answered clinical questions regarding their age of first opioid use and any secondary drugs of abuse. Patients were considered to be poly-drug users if they reported another drug of concern other than alcohol or other types of opioids. All participants were administered the Intolerance of Uncertainty Scale (IUS), the Barratt Impulsivity Scale (BIS-11), and the State Trait Anxiety Inventory for Adults (STAI). Eleven participants were not included in the analyses of certain measures due to failure to complete all the questions on the IUS (n = 4), STAI (n = 2), or BIS-11 (n = 5). Data from these participants were included in analyses that did not involve the incomplete questionnaire. The Intolerance of Uncertainty Scale (IUS): The IUS is a 27-item self-report scale measuring negative beliefs about the nature of uncertainty and its consequences [18]. The extent to which the respondent agrees with each item is rated on a 5-point Likert-like scale (1 = not at all characteristic of me to 5 = entirely characteristic of me). The IUS assesses the belief that uncertainty has negative behavioral and self-referent implications, and that uncertainty is unfair and spoils everything. The IUS has been strongly correlated with GAD, worry, anxiety, and depression, and has shown excellent internal consistency (α = .94) and good test-retest reliability (r = .74) [19]. The Barratt Impulsivity Scale– 11th revision (BIS-11): The BIS-11 is a 30-item self-report measure which evaluates impulsivity as a multifactorial behavioral and personality construct [53]. It assesses attentional impulsivity (inability to focus attention/concentrate), motor impulsivity (acting without thinking), and non-planning impulsivity (difficulty planning and thinking carefully about the future). Respondents rate whether a statement reflects the way they act and feel on a 4 point scale (1 = rarely/never to 4 = almost always/always). The BIS-11 is the most widely used measure of impulsiveness, and shows strong internal consistency (α = .83), retest reliability (r = .83), and strong convergent validity with other self-report measures of impulsiveness [37]. The State Trait Anxiety Inventory for Adults (STAI): The STAI is a 40-item self-report questionnaire measuring state anxiety (transient emotions elicited by specific scenarios) and trait anxiety (a relatively consistent predisposition to react to circumstances in an anxious way) [54]. The STAI is comprised of two forms: Form Y-1 assesses state anxiety, and was not administered in this study. Form Y-2 assesses trait anxiety and requires respondents to indicate on a 4-point scale whether a statement reflects how they feel generally (1 = not at all to 4 = very much so). Form Y-2 shows strong internal consistency (α = .89) and retest reliability (r = .88) [55]. The IBM SPSS Statistics version 24 was utilized for the statistical analysis. Independent-samples t-tests were used to assess mean differences in age and years of education between sample groups. The frequency of males and females were analyzed with the chi-square test using Yates’ correction to adjust p values for a 2x2 table. Independent-samples t-tests were used with poly-drug use as the independent variable and scores on the IUS, BIS-11, and STAI as dependent variables. Partial correlations controlling for age, years of education, and gender were employed between all scales. Two hierarchical moderation regression analyses were conducted to determine the unique contribution of addiction status, impulsivity and anxiety variables to IU. A hierarchical regression analysis was also utilized to test for a mediation effect of anxiety on the relationship between impulsivity and IU.
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