Nationality is only one variable among others, and I think that it is generally given too much weight in Academia, public and private sector policy-making, and in popular (mis)conceptions about the human species. What is legitimate, useful, and pertinent in the design of a project depends on your research objectives, scope, and feasibility, within existing limitations.

Nationality can have explanatory power but it's ultimately incumbent on the researcher to justify its use as a predictor theoretically. It may also prove advantageous to use different regions, as indexed by regional codes, the predictor variable; previous research has had success with it (e.g., Murray, Trudeau, & Schaller, 2011; Schaller & Murray, 2008). Within country variation is also helpful but, again, its use is justified by theory above all else.

There have been some studies looking at country-level differences in certain dispositions (e.g., conformity proclivity; Murray et al., 2011) but, the better predictor of personality variation geographically would looking at individual regions. I also give this answer with the theoretical orientation of personality being an outgrowth of culture, which is the mediating link between personality and environmental factors (i.e., evolutionary account). Just always consider theory in conjunction with methodological recommendations.

Dear Pavlo.

If I understand it well you refer to three positions and findings regarding the issues you raise.

As you say, Fischer and Schwartz (2011)  found more consensus (than disagreement) on values across countries. In contradistinction, Kirkman, Lowe and Gibson (2016) claim that a relatively limited part of the overall variation in cultural values resides between countries, and over than 80% resides within countries. Finally you say that Beugelsdijk, Kostova and Roth (2016) propose that researchers should use the interaction between country level cultural variables (e.g. Hofstede scores) and cultural tightness to correct for the degree of consensus in a country.  After this, you raise two questions: 1) Is it still legitimate to use country level cultural scores as explanatory variables? 2) What about personal traits and attitudes, for example, what about the level of happiness?

I am sympathetic with Beugelsdijk et al.' position because it appeals to a kind of a tertium between the other two relatively opposite positions. It seems relatively  obvious that nationality is, among others, an explanatory factor of individuals' values, personal traits, and attitudes. Think, for example of moral values. If you are acquainted with Richard Shweder' s work on the big three of morality, then you know that the majority of Western societies give a great importance to the sense of individuals' autonomy and rights. In contrast to this, Easter societies give a great importance to the sense of individuals' community and one's duties towards the several groups wherein s/he is immersed. Highly religious countries are oriented say, to the divine law. To be moral, in this case, is to follow divine commandments and laws.

Note also that values could be seen, for example, in terms of morality (e.g, not to treat others unfairly-- see L. Kohlberg's (1984) theory of morality -- not to turn away from someone in need -- see for this respect C. Gilligan's (1982) theory on an ethic of care or responsibility -- social conventions (e.g., ways of dressing or addressing; see for this respect E. Turiel's (1983) thinking on the individual's distinction between morality and convention), and the personal sphere or the sphere that belongs to individual's jurisdiction area (e.g., to choose one's friends -- see for this respect, L. Nucci's (2004) thinking of the personal domain. There is amassing evidence that shows that social conventions and personal values vary more than moral values across countries. What about the values related to, say, the truth and the beauty domains. There is also amassing evidence that shows that what is considered to be true varies less across countries than what is considered to be beautiful. Note that the true, the good, and the beautiful are universal categories, regardless of how they are seen at different places and times .You refer to values, personal traits, and attitudes. But what values (moral, conventional, aesthetical, ecological, economic) are  you thinking of?) The same could be said regarding personal traits (e.g.. introversion, extroversion) and attitudes (e.g. pro-social, anti-social, patriotic, non-patriotic). All of this means that a comprehensive answer to your questions would imply to write one or several books. Because of this, my answer to your question is a short answer.

Even so, I hope that my previous considerations are of some help for you. Of course you will be able to take into account the wise previous answers and the possible subsequent ones.

Best regards