To our knowledge, this is the first study of its kind from Pakistan investigating the prevalence of ego defense mechanisms employed by medical students. Two major studies with similar objectives employing the DSQ-40 have been previously published [24, 25].
The three main themes, reflecting the most prevalent mechanisms, representative of the characteristics of the Pakistani medical student population were:
Rationalization, defined by the DSM as, 'offering a socially acceptable and apparently logical explanation for an act or decision actually produced by unconscious impulses', was the most commonly employed ego defense mechanism by the participating medical students. The authors observed rationalization, which is an immature factor, to be more common among first and second year students than those in their clinical years. This finding may be explained by a study assessing the developmental aspects of psychological defenses which indicates that defense mechanisms tend to mature with advancement of age in adolescents to young adults .
Defined as 'anticipating consequences of possible future events and considering realistic, alternative responses or solutions', this was found to be the second most common ego defense mechanism with a mean score of 6.34 ± 2.44. A similar observation has been reported by La Cour  in Danish medical students. It was found to be so independent of gender and year of education. However, there was significant difference between private and government institutions, with Anticipation more commonly employed by government college students. As mentioned above, government institutions offer greater subsidization of tuition fees, catering more widely to students with a lower socioeconomic status. We may suggest that these students may be forced to face the harsh realities of life sooner than their rich counterparts.
Before undertaking the current study, the authors hypothesized that Undoing was a rarely employed neurotic defense. However, it was observed to be the third most prevalent mechanism with a mean score of 5.93 ± 2.67, and was employed more commonly by females and students of the clinical group. In the questionnaire, it deals with undoing of aggressive behavior (e.g., Item 32: After I fight for my rights, I tend to apologize for my assertiveness). This finding may be explained by the 'hierarchical' nature of the extremely 'competitive' medical profession where "Undoing could be seen as a submissive, but adaptive, strategy in the field of competition. The 'fight for rights' is not a suitable attitude in an authoritarian environment", La Cour  aptly summarizes.
Clinical vs. Preclinical
In this study, the authors observed a greater prevalence of immature and neurotic factors amongst students in their preclinical years. The general maturity of the psychological defense mechanisms is found to change over a lifespan . In this study, however, there is only a minor age difference between the two groups. Hence, the inference that defense mechanisms mature with age and added responsibility in clinical years may be overzealous.
The differences in the prevalence of these defenses may then be explained by the increased levels of stress and the overall psychological maturity in senior medical students. Chronically persistent high levels of stress coupled with greater exposure and general maturation of the psyche may reflect the higher utilization of mature defense styles in this group of students.
A study conducted in Karachi investigating a similar population of medical students concluded that fourth and final year students showed a greater tendency to feel stressed (95% and 98% respectively) than students of other years . Preliminary data of one particular study  assessing the level of distress in medical students in a pre-exam and normal school setting support the view that, upon entering medical school, students' emotional status resembles that of the general population. However, the rise in depression scores and their persistence over time suggest that emotional distress during medical school is chronic and persistent rather than episodic.
Among individual neurotic ego defense mechanisms, the mean scores of Undoing, Reaction formation and Idealization were significantly higher in students enrolled in their preclinical years. Splitting and Rationalization were the most prevalent immature defenses in this group. These findings may be explained, albeit cautiously, by the fact that Pakistani first and second year medical students are teenagers aged 17 to 19, at a point where their personalities are being molded and various life events tend to leave very strong impressions. These impressions are either completely positive or negative, and it is only with time and maturity that they learn to see the grayer shades of life.
Neurotic mechanisms were found to be more commonly employed by females, whereas the use of immature defenses was prevalent among male medical students.
The positing of gender differences in defenses on the basis of classical psychoanalytic theory  has generally been supported in prior investigations, which state that women tend to use internalizing defenses such as Introversion, and men are more likely to employ externalizing ones [28–30] such as Projection and Aggression [30–32].
In our study, the mean score of Isolation was found to be significantly greater in males than females. This is consistent with findings made by Watson and Sinha  and La Cour . Females are generally more emotionally labile as compared to their male counterparts who are better at splitting emotional components from their thoughts , as shown by higher means for Isolation in men in our study.
The authors observed that female students employed Somatization more commonly than male students; also reported by La Cour . These higher prevalence rates may be explained by women's greater psychological awareness of their bodily functions and reactions. Gender variations were also found in Undoing, Devaluation and Idealization defense mechanisms; however, these variations were inconsistent with those reported in prior studies.
Andrews et al  did not find any differences in the ego defense mechanism employed by the two genders. Studies by Watson, Sinha and La Cour, along with our own results do not support his findings. The authors support the suggestion made by Watson and Sinha that specific norms of the DSQ-40 need to be reconstructed with regards to gender.
Ego defense mechanisms are unconscious processes [1, 6], and thus are not obviously amenable to measurement using self-report questionnaires. Nonetheless, they manifest as 'typical behaviors' in response to stress, which an individual is capable of reporting,  even if they lack insight into the defensive function of that behavior 
Even though the DSQ is a self-reporting tool offering portability, affordability, and quantification, it faces significant challenges in the domains of reliability and validity by virtue of the intrinsic complexity of defense mechanisms . The DSQ-40, which has been used in a number of studies along similar themes, still remains under investigation. Trijsburg and colleagues  have emphasized that the validity of specific defenses, as demonstrated in this present study, is weak and that evidence for classifying defenses using this tool into immature, neurotic, and mature types is lacking. However, the DSQ, they conclude, remains a useful instrument for determining overall defensive functioning.
Subsequent to prior numerous revisions [4, 23, 31, 33], recent efforts to improve the reliability, validity, and congruency of the tool with the DSM-IV resulted in the development of the DSQ-60 . However, preliminary results show that the psychometric properties of the scale remain inadequate for broad use recommendation.
There is a lack of normative data on ego defense mechanisms employed by the general population of Karachi. As our data was collected from five different medical colleges of Karachi, it would be safe to say that our results can be generalized to represent the entire medical student population of Karachi, if not Pakistan. The overrepresentation of women in the sample is a simple reflection of the fact that an increasing percentage of medical students worldwide are female [37–39], and that a large proportion of the future physicians of Pakistan will be females. This highlights the importance of identifying the differences in psychological defense mechanisms employed by the two gender groups.
Our cross-sectional study design was limited in several aspects. Although this method is simple, convenient, and economically feasible, a temporal or causal relationship between stress levels and ego defense mechanisms can not be established based on these results. Furthermore, it is imperative to remember that the current study focused on medical students only, and hence, the results may not be applicable to the general population.