Some discussion at Mangan's prompted me to look for studies comparing Europeans of various nationalities on tests of musical aptitude. I found a summary of several such studies in a 1955 book:

In a Chicago Jewish orphanage and a Chicago public school, children numbering 550 were given both the Sea shore and the Kwalwasser-Dykema Music Tests. The national and racial groups reported by Sanderson 146 are Jewish, German, Negro, Italian, and Polish. In order of standing, the Jewish group rated highest, followed by German, Italian, Negro, and last, Polish, who showed marked inferiority. In this study the Negroes earned the highest score in rhythm. The total mean scores of the Sanderson study follow: Jews 185.5; Germans 183.2; Negroes 180.6; Italians 178.4 and Polish 173.7.

The Witherson 188 study, a survey of all the children in the grade schools of Duquesne, Pennsylvania, numbering approximately 2,000 children, employed the Kwalwasser-Dykema Music Tests. More than a dozen different national and racial classifications were represented, and although the Sanderson and Witherson studies were conducted in communities separated by considerable distance the resemblances are striking. In descending order of achievement, the groups rate as follows: Jewish, native American, American foreign-born, Scotch-Irish, Welsh, German, English, mixed foreign, Serbian-Croatian, Russian, Polish, Hungarian, Lithuanian, Slovak, Italian, and Negro. The averages (means) of the Witherson study are presented for comparison with the Sanderson study: Jewish 185.9; German 183.5; Polish 180.5; Italian 178.2; and Negro 177.0. The Eneboe study of 740 Chicago high school students yielded similar results with the same music test. Scandinavian, English, and German children ranked high; the Slavic group was about 20 points lower, and the Italian and Negro children were very low.

Finally, the author wishes to present Dykema's 29 study of ten European groups, numbering approximately 6,000 children of secondary school age, measured abroad. While on sabbatical leave from Teachers College, Columbia University, in 1930-31, he gave the tests in ten different countries under conditions that were maintained fairly constant from place to place. The countries represented in his investigation were : Germany, England, Scotland, Czecho-Slovakia, Russia, Italy, Hungary, Austria, Ireland, and France. It would be foolhardy to accept his results without qualification, for an average sampling of only 600 children in each country can hardly be considered adequate. Yet the study is unique and, as test populations go, rather authoritative. The total mean scores earned by the ten groups are:

Country Mean

Germany 193.58
England 193.42
Scotland 193.42
Czechoslovakia 193.03
Russia 192.40
Italy 192.29
Hungary 189.25
Austria 188.98
Ireland 185.33
France 183.14

All countries 191.21

When we compare the scores of children abroad with those of our own country, we find that the average European child earns roughly ten points more. This difference is based upon the measurement of 4,250 American school children tested with the Kwalwasser-Dykema Music Tests about the same time that Professor Dykema was testing abroad. Statistically the difference is large enough to be considered significant. In addition, we note that foreign children show greater variation in their scores; European scores are more heterogeneous and ours more homogene ous. The standard deviation for all European children is 18.70; for American children 16.49. One-third of the children above the average and one-third below the aver age earn between 191. plus 18.7 and 191.2 minus 18.7. American children with their average of 180.9 show a variation of 16.5 above and below the mean. These scores showing less variation support the claims of anthropologists that hybridization is moving at a rapid rate in our country. Sharp national lines of cleavage are being eradicated to a great extent by the forty million immigrants who have settled here in a single century from 1830 to 1930.

[Jacob Kwalwasser. Exploring the Musical Mind.]
For comparison, here is Mangan's breakdown of Charles Murray's list of "significant" composers by national origin:
24 German
16 French
12 Italian
6 Russian
2 Czech
2 English
2 Hungarian
1 Dutch
1 Flemish
1 Norwegian
1 Polish
1 Swedish
Apart from Germany appearing near the top of both lists, within Europe there seems to be little relationship between the number of great composers produced by a country and the average raw musical talent of (modern representatives of) its people.