1. Introduction
Procrastination is defined as voluntarily delaying a task despite knowing that there will be negative consequences for the delay. For procrastination assessment, there is an online survey with three main scales: Adult Inventory of Procrastination (AIP), Decisional Procrastination Questionnaire (DPQ), and General Procrastination Scale (GPS). The items of these three scales are used in a 12-item scale called Pure Procrastination Scale (PPS) with a high internal consistency (α=0.92), and good convergent validity with Irrational Procrastination Scale (IPS), Susceptibility to Temptation Scale (STS), and Satisfaction with Life Scale (SWLS). Rebetez et al found two factors in the French version. However, the Swedish version of PPS has a factor structure similar to that of the English version. For the Norwegian version, a study showed that PPS was a unifactorial scale, while another study on the validity of PPS along with IPS and STS using more heterogeneous samples from six European countries indicated a fourth model representing three related but different dimensions: delay in decision making, irrational delay in activities, and delay in meeting deadlines. Their results suggested that the three-factor model had a better fit. The current study aims to examine the psychometric properties of the Persian version of PPS.
2. Materials and Methods
In this study, participants were 400 students who were selected from the Tehran University of Medical Sciences, Iran University of Medical Sciences, and Islamic Azad University of Science and Research Branch using a multi-stage cluster sampling method. The inclusion criteria were age ≥18 years and being a college student. Exclusion criteria were: any physical disability and unwillingness to sign the informed consent form, and return of incomplete questionnaire
The authors first asked for permission of Dr. Piers Steel who developed the PPS. Then, the questionnaire was translated from English into Persian. Three PhD students and three professors in Psychology reviewed the initial translated version. Afterwards, a Persian-speaking professor in English literature, who had not previously read the original version, translated the Persian version back to English. Then, a panel of experts in psychology compared the original and translated versions so that there was no difference in the meaning between them 
Before data collection, the study was approved by research ethics committee of Iran University of Medical Sciences (Code: IR.IUMS.REC.1397.647). A written informed consent was obtained from all students after explaining the study objectives and procedures to them and assuring them of the confidentiality of their information. Participants were asked to fill out the battery of four self-report measures, PPS, Difficulties in Emotion Regulation Scale (DERS), Depression, Anxiety and Stress Scale-21 (DASS-21), and SWLS. 
Exploratory Factor Analysis (EFA) with maximum likelihood estimation was performed to evaluate the factor structure of the Persian PPS. Then, an invariance test was carried out to analyze the factor invariance of the three-factor structure of the Persian PPS based on gender, age and marital status. Validity was determined by assessing the correlation of the Persian PPS and its subscales with SWLS, DASS-21 and DERS. Cronbach’s alpha was calculated for determining the internal consistency of the questionnaire. Moreover, for assessing the test-retest reliability, 50 other college students were recruited to complete the Persian PPS. The interval between two evaluations was two weeks.  
3. Results
Of 400 participants, only 390 completed the questionnaires where 207 (53%) were male and 183 (47%) were female. Their mean age was 24.77±5.32 years (ranged 18-50 years); 89% were single and 11% married; 5.6% were associate students, 52.6% undergraduate students, 35.4% graduate students, 1.5% MD students, and 4.9% PhD students.
Cronbach’s alpha for three subscales of decisional procrastination, implemental delay, and timeliness and for overall Persian PPS was 0.83, 0.90, 0.85, and 0.94, respectively, indicating acceptable internal consistency. The test-retest reliability for decisional procrastination, implemental delay, timeliness, and for overall Persian PPS were 0.81, 0.80, 0.79 and 0.88, respectively (P<0.001). The DERS had the strongest correlation with the Persian PPS. As shown in Table 1, correlations between the subscale scores of PPS and the scores of DERS, DASS-21, and SWLS were statistically significant.


The Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy and Bartlett’s test of sphericity showed that the 12 items of the Persian PPS were adequate for factor analysis (KMO=0.946, Bartlett’s χ2=3576.70, P<0.0001). Figure 1 shows the factors with eigenvalues >1. In EFA of PPS structure, three factors of decisional procrastination, implemental delay and timeliness were extracted. The eigenvalues of these factors were 3.197, 2.551 and 2.413, respectively. These three factors together explained 68.013% of the overall variance of PPS structure. The factor loads of all the items were >0.4.
To investigate the invariance in factorial structure of the Persian PPS based on demographic variables (gender, age, and marital status), multi-group confirmatory factor analysis was carried out. The results showed the between-group invariance of the factor structure, measurement weights, structural covariances, and measurement residuals of PPS across demographic variables (Table 2).


4. Discussion
Results of this study showed the high internal consistency of the Persian PPS and its three subscales of decisional procrastination, implemental delay, and timeliness with Cronbach’s alpha coefficients of 0.83, 0.90, and 0.85, respectively, which is consistent with other versions of PPS. For example, the Korean version has a Cronbach’s alpha of 0.93 and for the French version it is in a range of 0.77-0.90 [26 ,14 ,12]. 
EFA results confirmed the three-factor solution of the questionnaire, which is consistent with  the results of Svartdal et al, and is in disagreement with the two-factor model of French version. The Persian version of the PPS consisted of three factors; decisional procrastination (putting off irrational decisions), implemental delay (voluntary delay of actions), and timeliness (not being able to meet deadlines). These factors are in the original version of the PPS derived from DPQ, GPS and AIP [11]. The result of this study is in line with early speculations that procrastination is a multidimensional concept. 
The total score of PPS and its subscales had a significant correlation with the scores of DERS and DASS-21. The strongest correlation was found between the scores of DERS and PPS. This is in consistent with studies suggested that negative emotions are antecedents of procrastination. Eckert et al. found that enhancing emotion regulation skills can reduce subsequent procrastination.
As expected, there was a significant negative relationship between the scores of SWLS and PPS, implying that PPS and SWLS measure contrasting constructs. This is also consistent with previous studies [12 ,10]. Beutel et al. found out that procrastination is associated with depression, anxiety, and stress, which in turn decreases life satisfaction, particularly in terms of work and income.
One of the limitations of this research was the study on students. There are higher rates of depression, anxiety and stress among students. They were also at low age (24.77±5.32 years). Therefore, caution should be exercised in generalizing the data. Since the clinical information of the students were not surveyed, further study is recommended to compare clinical and non-clinical samples and determine the minimum clinically important difference.

Ethical Considerations
Compliance with ethical guidelines
The study was approved by the research ethics committee of Iran University of Medical Sciences (Code: IR.IUMS.REC.1397.647). 

Funding
This study received financial support from Iran University of Medical Sciences, School of Behavioral Sciences and Mental Health (Tehran Institute of Psychiatry).

Authors contributions
Conceptualization, initial draft preparation, data collection, and data analysis: Leili Jamil and Somayeh Zamirinejad; project administration and supervision: Ahmad Ashouri. Read and approved the final version of the manuscript: All the authors.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the staffs of Iran Medical Sciences University, Tehran University and Islamic Azad university of Tehran. This work would not have been possible without their cooperation during the implementation phase.


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