Extended Abstract
1. Introduction
The past decade has witnessed a noticeable increase in empirical research devoted to understanding the dark aspects of personality. The research has expanded in spite of no clear consensus on the number and nature of aspects of the personality who should be considered dark. Those dark aspects of personality that have been the focus of empirical research in the last decade include dark triad personality consisting of narcissistic, psychopathic, and Machiavellianism traits.
The similarities and differences between the dark triad traits of personality were expanded by Paulhus and Williams, who invented the term "dark triad traits" of personality. Dark personality features are socially aversive and associate with various interpersonal challenges and potentially destructive behaviors (e.g. aggression, manipulation, exploitation). For example, certain dark personality features are associated with the perpetration of sexual violence. Researchers have argued that one or more of these characteristics may determine the core of the dark triad traits, but explorations have led to controversy over the term ‘to reach the core’. Disagreement over the core of the dark triad traits of personality is partly due to the fact that these 
Although there are significant similarities between the components of dark triad of personality, we must acknowledge the important differences between these components. Therefore, due to the wide and different links of the dark triad of personality to other constructs, the number of dark traits may be more than three. There have been recent suggestions to expand the Dark Triad into the newly christened Dark Tetrad with the inclusion of sadism. Sadism means to enjoy the suffering of others. This phenomenon is often discussed in its severe form in relation to sexual and sexual contexts.
Recently, Pinker has suggested a milder form of this phenomenon, called "soft sadism" or "everyday sadism." This often appears as a non-sexual abuse and is common in different people in different societies; it also seems that statistical data is distributed naturally. Sadistic people always look for opportunities to engage in cruel or abusive daily activities. It should be noted that as compared to psychopathic people who do not care about others in their interpersonal relationships, sadistic individuals may harm others through their selfish goals.
Although authors of the dark traits recognized the formulation of the dark tetrad at the theoretical level, there is still insufficient empirical evidence for empirical acceptance of this formulation. Of course, it should be stated that various tools are available for evaluation of everyday sadism, but for the development of dark triad to the dark tetrad, separate measurements of the sadism component will not be useful. It should be evaluated in the context of the dark triad traits and more importantly, its role in validating the concept of the dark tetrad traits, in order to judge the validity and reliability of the dark tetrad. Since there is no comprehensive and unitary tool that can be used to evaluate the dark tetrad personality, this research is in line with the formalization and theoretical extension of the dark triad to the dark tetrad. For the first time, the dark tetrad personality was validated using the Persian version of the Dirty Dozen Inventory, along with the Persian version of the Short Sadistic Impulse Scale. Therefore, the aim of the current research was to study the validity of Dark tetrad personality traits model among Iranian population. 
2. Method
This research uses a descriptive-survey method that evaluates the validity of a psychometric instrument. The statistical population consisted of all undergraduate students of Urmia University. This cross-sectional study was implemented on 500 undergraduate university students in the academic year 2016-17. Samples were selected using stratified sampling method and were assessed using the Persian version of Dirty Dozen Scale and Short Sadistic Impulse Scale (SSIS). Inclusion criteria included undergraduate education, absence of academic failure, and willingness and informed consent to participate in the research. The exclusion criteria included lack of cooperation, mismatch of the questionnaires, the occurrence of acute psychiatric disorder, and drug use based on self-declaration.
3. Results
The mean (SD) of the age for boys was 21.35(2.33) and 21.38(2.19) year for girls. For the test of construct validity of dark tetrad, personality traits model was used for confirmatory factor analysis that showed dark tetrad model is confirmed and has a good fitness to data. The results of this analysis supported the four-factor structure of dark tetrad model. Also, Test-retest correlation coefficients for the total scale and its subscales ranged from 0.76 to 0.84. Internal consistency for the total scale and its subscales ranged from 0.68 to 0.88. 
4. Discussion
The present research was conducted for the first time in Iran for validation of the dark tetrad model in a sample comprising of undergraduate students. This study combines the Persian version of the Dirty Dozen Questionnaire, which is a short and effective tool for measuring the dark triad with the Persian version of short sadistic impulse scale, to test the validity of dark tetrad model. Dark tetrad personality traits model was confirmed among Iranian sample and had a good fitness to data. The model of dark tetrad in Iranian culture was confirmed and had a similar structure to the findings from the body of research in this field. Based on the results of this study, it can be suggested that the measurement of the dark tetrad of personality and also the formulation of problems of individuals, especially interpersonal problems based on the model of dark tetrad in clinical and research positions can be useful.
Ethical Considerations
Compliance with ethical guidelines
Regarding ethical considerations in the research, the subjects were asked to complete the questionnaire without name and the informed consent was obtained for participation in the research.
Funding
This research was extracted from the MA thesis of the second author in the Department of Clinical Psychology, Urmia Branch, Islamic Azad University, Urmia, Iran.
Conflict of interest
The authors declared no Conflict of interest.
Acknowledgements 
We are grateful to the undergraduate students of Urmia University who participated in this research.

 

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