How do we determine "population statistics" for population-dependent Halachot?

Question

There appear to be several halachot that are based on "a majority of Israel". For example:

Mishnah Berachot 54a:

הרואה מקום שנעשו בו נסים לישראל אומר ברוך שעשה נסים לאבותינו במקום הזה

IF ONE SEES A PLACE WHERE MIRACLES HAVE BEEN WROUGHT FOR ISRAEL, HE SHOULD SAY, BLESSED BE HE WHO WROUGHT MIRACLES FOR OUR ANCESTORS IN THIS PLACE (Soncino translation, capitals in original).

The Talmud there qualifies this:

אמרי אניסא דרבים כולי עלמא מיחייבי לברוכי אניסא דיחיד איהו חייב לברוכי

The answer [is that] for a miracle done to a large body it is the duty of everyone to say a blessing, for a miracle done to an individual he alone is required to say a blessing. (Soncino translation)

Rabbeinu Yonah there defines a ניסא דרבים as a miracle that was done for all or most of Israel:

כלומר שנעשה לכל ישראל או לרובן

So let's imagine that a major miracle occurred. How would we know if it meets the threshold of "most of Israel"? Are we expected to travel the entire world to figure out the Jewish population and then calculate whether the miracle occurred to > 50% of that number? Are we just supposed to assume that it was not "most of Israel" unless it is glaringly obvious (e.g. millions of Jews were together such that it is virtually impossible that this is not the majority)? Or is perhaps the threshold of "most of Israel" not exactly precise and it does not actually require a technical majority? Or perhaps it only refers to certain Jews (e.g. those living in the Land of Israel)?

Are there any sources that discuss the parameters of "most of Israel", or how we would go about determining if the threshold was reached?

Note that an answer need not address the specific case above. There are other situations where this could be relevant as well. For example, the Sefer Hachinuch writes by a bunch of mitzvot that they are applicable בזמן שרוב ישראל על אדמתן – when the majority of Israel is in its land (e.g. Mitzvah # 95).

Answer 1

In the case of when most of Israel sinned in a way requiring a par helem davar, a communal sin offering, a simple absolute majority of the people in the Land of Israel is required. That is, if there are 600,001 people and 300,001 of them transgressed, the sacrifice is brought, assuming all other requirements. (In this particular case the division of the twelve tribes is relavant, and seven complete tribes would also be considered most of kahal for this sacrifice.)

The Rambam (Shgagos 13:2) codifies this rule:

עָשׂוּ רֹב אַנְשֵׁי אֶרֶץ יִשְׂרָאֵל עַל פִּיהֶם. אַף עַל פִּי שֶׁאֵלּוּ הָעוֹשִׂים שֵׁבֶט אֶחָד. וְכֵן אִם עָשׂוּ רֹב הַשְּׁבָטִים אַף עַל פִּי שֶׁהֵן מִעוּט הַקָּהָל. בֵּית דִּין חַיָּבִים וְהָעוֹשִׂין פְּטוּרִין. כֵּיצַד. הָיוּ יוֹשְׁבֵי אֶרֶץ יִשְׂרָאֵל שֵׁשׁ מֵאוֹת אֶלֶף וְאֶחָד. וְהָיוּ הָעוֹשִׂין בְּהוֹרָאַת בֵּית דִּין שְׁלֹשׁ מֵאוֹת אֶלֶף וְאֶחָד וַהֲרֵי כֻּלָּן בְּנֵי יְהוּדָה בִּלְבַד. אוֹ שֶׁהָיוּ הָעוֹשִׂים בְּנֵי שִׁבְעָה שְׁבָטִים כֻּלָּן אַף עַל פִּי שֶׁיֵּשׁ בָּהֶן מֵאָה אֶלֶף. הֲרֵי בֵּית דִּין חַיָּבִין וְכָל הָעוֹשִׂים עַל פִּיהֶם פְּטוּרִין. וְאֵין מַשְׁגִּיחִין עַל יוֹשְׁבֵי חוּצָה לָאָרֶץ שֶׁאֵין קָרוּי קָהָל אֶלָּא בְּנֵי אֶרֶץ יִשְׂרָאֵל.

If most of the people of the Land of Israel did (the transgression) on (the Sanhedrin's) word, even if theses actors are one tribe, and also if most of the tribes did, even though they are the minority of the Congregation, the Court is obligated (to bring a communal sacrifice) and the actors are exempt. How is this? If the residents of the Land of Israel were 600,001, and the actors by the ruling of the Court were 300,001 and they were all from the tribe of Judah alone, or if the actors were seven whole tribes, even though they are (only) 100,000, the Court is obligated and all of the (individual) actors by their word are exempt. And we do not pay attention to residents of (countries) outside of the Land, for the "Congrenation" only refers to the people of the Land of Israel.

Answer 2

I do not have sources but I my Rav told me that "beged isha" for a man is dependent upon whether or not it is a norm for men to dress or do the clothing or act in question, and he said that it goes by the norms of society as a whole, not just Jewish people.