A trade union is an organization of wage-earners in the same handicraft or occupation. Unions exist among workers in all the old distinctive handicrafts, such as the printers, stone cutters, cigar makers, carpenters and in many other groups such as musicians and retail clerks. The local chapters in many cases have been long united in national unions (often international, including the United States and Canada). An industrial union is one that seeks to unite all workers employed in the same class of establishments regardless of their craft or the kind of work they do. The most notable examples are the United Mine Workers, the Brewery Workers, and the Industrial Workers of the World. In 1881 a number of national trade unions united for certain purposes, to form the American Federation of Labor with a membership of about a quarter million workers, which has steadily increased since that date. The American Federation of Labor now includes also some important unions of the industrial type. Several strong national trade unions (the most important being the brotherhoods of railroad employees) are not affiliated with the American Federation of Labor. § 5. #Statistics of labor organization.# The ratio of organized workers to the population is estimated (figures for 1910) to be highest in the United Kingdom, being nearly 7 per cent; it is next highest in the German Empire, being nearly 6 per cent; whereas, in the United States, it is but 2.3 per cent. This difference is largely due to the much greater relative importance of agriculture in the United States. The total membership of trade unions in the United States and Canada is estimated to have been in 1910 about 2,200,000, of which only about 100,000 were in Canada. This was 5.5 per cent of all persons (38,130,000) gainfully employed, or 6.8 per cent of male employees, and 9 per cent of female employees. Organization was very weak (less than 1 per cent) among the workers in a group of industries occupying nearly one-half of all workers, including agriculture, the hand trades, oil and natural gas, salt, and rubber factories. Organization was not of large extent (1 to 10 per cent) in other groups of industries occupying more than one fourth of all workers, including those engaged in producing quarried stone, food stuffs, iron and steel, metal, paper and pulp, stationary engineers, in public, professional, and domestic service, and in clerical work. Organization was of much greater strength, including 10 per cent or more of the workers, in the remaining industries and occupations.