First, a major caveat: a less-than-30-second video clip of Monk in a particularly stressful context is insufficient basis for trait judgments, according to trait theory, which defines traits "as habitual patterns of behavior, thought, and emotion. According to this perspective, traits are relatively stable over time" (Kassin, 2003). Since this clip doesn't afford the opportunity to observe Monk over time, it's dangerous to assume his eccentric behaviors are a result of his personality, not of his circumstances. Most people could find themselves behaving thusly in the right circumstances. BTW, I acknowledge that outside of this clip's context, Monk's (fictional) behavior is often stably similar to this. This point is mostly meant to dissuade application of my points to other cases where context outside a 30-second observation is unavailable. That's not to say personality is entirely unobservable in such a short time though, just that it's difficult. You may want to read about the Realistic Accuracy Model of personality judgment (Funder, 1995, 1997) for a sense of when you can pick up on personality generally.
Second, you might try directing this to the Movies & TV Stack Exchange as well (or instead, if you wish), since Monk is a popular fictional character, and people over there probably love questions like this (can't say for sure, as I haven't spent much time there myself). That's not to say I mind answering here though. I also see you have three upvotes from our community already (make that three plus mine, and one unexplained downvote—shame on them :P ). I appreciate your genuine interest in our perspectives here!
Third, assuming strictly for the sake of argument that his behaviors do reflect his basic tendencies and characteristic adaptations (for context on these terms, see McCrae & Costa, 1999), and not other endogenous causes like physiological conditions (e.g., Parkinson's disease, low blood glucose, drugs)...I can first note that this is a relatively good situation for making trait judgments, in that it's unstructured, hence there's freedom for self-expression (Snyder & Ickes, 1985; Funder & Colvin, 1991), and in that it's an emotionally arousing situation, hence it provokes personality expression.
- The strongest eccentricity I note is the fidgeting. (BTW, I focus on strong eccentricities in general because normal behaviors are somewhat less diagnostic of traits, and more ambiguous for their inseparability from behaviors prescribed by social norms.) To me, fidgeting is a signal of high emotional arousal, and probably also slightly negative emotional valence (see the diagram of the circumplex model of emotion I included in this answer). Again, this could just be an emotional state, but assuming it's trait-level negative emotionality, this may imply neuroticism.
- Self-doubt is also characteristic of definitionally neurotic individuals—e.g., Woody Allen, or at least his public persona...though Wikipedia notes self-described phobias, which relate to neuroticism too. I wouldn't call this a phobia in "unsure Mr. Monk's" case though :) nor would I be sure that it's a result of his probable neuroticism. As a detective, it's his job to reason carefully and objectively. I probably should've mentioned before that we need to consider (and control in any statistical model) the stable influence of social roles when making judgments about role-relevant traits like self-doubt too. In this case, I'd read more into his personality from his initial certainty, which he then tempers with reason.
In contrast to self-doubt, the initial self-assurance that he later judges to be inappropriate reminds me of "black-and-white" thinking (a.k.a., splitting). To some extent, we all do this initially, as it takes time to elaborate our initial reactions into probabilistic, pluralistic, or otherwise non-absolute judgments. When we act on these thoughts without inhibition, though—even if we later renounce those actions on further reflection—that's another hint of high emotional arousal, and maybe neuroticism. Disinhibition can also indicate low conscientiousness or extraversion (which relates to positive affect, including enthusiasm and confidence to the extent that these are emotions).
However, knowing what I do about Monk outside this context, I wouldn't say he's extraverted or unconscientious. If anything, I'd say his quick switch from enthusiastic confidence (the eagerness in his "eureka moment") to self-doubt expresses a strong need for affect (see Maio & Esses, 2001). Basically, this is a trait-level motive to seek emotional experience, and relates to emotional intensity in general—both positive and negative. You can probably also infer this need from his initial decision to become a detective—it's very emotion-provoking work. Also, his self-checking behavior and thorough reconsideration of the situation—even delayed as it is here—is a marker of high conscientiousness. Both detective work and self-checking may also reflect strong needs for cognition and achievement.
- Considering that he does the most talking and is somewhat loud at times, we might have more reason to infer extraversion, because this relates to talkativeness and dominance somewhat. However, again, considering his social role, and the context of the TV series overall (most of which I haven't watched, TBH), I don't really think he's particularly extraverted. This is one of those personality cues we'd probably read too much into if we only had this brief video clip to judge, and nothing more. However, a strong need for power might be safe to infer here—again, especially in light of his career choice in law enforcement. He might even tend toward high authoritarianism, in as much as this trait entails tendencies toward favoring harsh punishment of rule-breakers and strict enforcement of societal law and order. Authoritarianism is very similar to social dominance orientation and related to conservatism, but I don't think we have much indication here of those traits.
Another source of information is his appearance. A colleague of mine, Laura Naumann(, Vazire, Rentfrow, & Gosling, 2009), would call the following static cues (as opposed to dynamic cues): he looks fairly healthy and neat (clean-shaven, clean clothes, buttoned shirt), and not what I would call fashionable. Here's what those cues indicated in Naumann and colleagues:
- Healthy: extraverted, stable, likable, confident, and less lonely
- Neat: extraverted, less open to experience, and less lonely
- Unfashionable - introverted, lonely
Mixed signals here overall, especially in the context of the behaviors we've covered so far. The only not-so-mixed signals seems to be "likable" and "not open to experience".
Your question itself provides some useful context: obsessive-compulsive personality disorder (OCPD). I add the "P" for "personality" here because I happen to know his obsessions and compulsions aren't specific, but generalized, and I've checked this against the show's premise according to Wikipedia. I'm no clinician, so I can't say for sure that he wouldn't get diagnosed differently by a professional (if he were a real person, not just portrayed by one). Then again, professionals often make mistakes, and as far as I know, this is one of the primary ways of distinguishing OCPD from OCD.
OCPD may be useful for trait inferences, because in theory (Widiger, Trull, Clarkin, Sanderson, & Costa, 1994), it is an expression of pathologically extreme traits: i.e., extremely high neuroticism and conscientiousness. This is why I don't think he's unconscientious, and again, another reason why we might be wrong to read low conscientiousness into his initial disinhibition. (Also, a good example of why stability is so important in judging traits!) OCPD may also relate to low agreeableness and openness to experience, and to high extraversion, but again, this is according to Widiger and colleagues' (1994) theory, as cited in The Personality Puzzle (Funder, 1997).
I express doubt because I tried to find an independent source for these relationships just now, and found Morey, Gunderson, Quigley, and Lyons (2000), which contradicts Widiger and colleagues (1994). Morey and colleagues' data shows a pattern of high neuroticism, low extraversion (i.e., introversion), and low agreeableness and conscientiousness in OCPD patients relative to community norms. Low conscientiousness is the main contradiction of Widiger and colleagues. The low extraversion contradicts my previous understanding too, but I expected low agreeableness and high neuroticism.
BTW, the distinction between OCD and OCPD is important for judging trait relationships, as Samuels and colleagues (2000) found some different relationships between OCD and the Big Five. Unfortunately, I don't think they report their data about relationships between OCPD and the Big Five...
In summary, that adds up to the following list of probable trait scores:
- High neuroticism and negative emotionality
- High conscientiousness?
- Monk's character seems based on the theoretical prototype of a conscientious person with OCPD (as in Widiger et al., 1994), but real people with OCPD tend not to be conscientious (Morey et al., 2000).
- Moderate-to-high extraversion?
- This doesn't sit well with me for Monk. It might be indicated in this clip, but it seems unlikely for a real OCPD case, and doesn't suit my impression of Monk in general.
- Moderate-to-low openness to experience?
- Indicated by his neat appearance, and maybe Widiger and colleagues' (1994) theory of OCPD
- Real people with OCPD seem to be relatively average on openness (Morey et al., 2000).
- Somewhat high needs for achievement, power, cognition, and affect.
- I know this theory a bit less well, but I'm comfortable saying he wouldn't score low on these.
- Maybe moderate-to-high authoritarianism?
- A loose inference based on his profession and other apparent traits.
- If I had to guess his political orientation from his traits, I'd say he's conservative. However, the show is set in San Francisco, which is relatively liberal, so this is also iffy.
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