A second characteristic of standard wage rates is that they may take the form of time-rates, or payment by results, or any combination of the two. Trade union agreements in the United States include all these varieties. It is true that a system of standard time rates is likely to be more in accord with the sentiment underlying the standardization movement. For under a system of payment by results individual differences in capacity are apt to be more readily reflected in the actual wage payments. And the sentiment underlying the principle of standardization is nearer the idea of equal payment for equal effort or equal sacrifice within the group, than the idea of equal payment for equal product. This is illustrated in the report signed by the Labor Members of the Committee on Industrial Relations (1912-16) in reference to the wage payment systems of scientific management which reads, "... All of these systems of (i.e., of scientific management) payment tend to center the attention of the worker on his individual interest and gain and to repress the development of group consciousness and interest. Where the work of one man is independent of another, the individual has no motive to consider his fellow, since his work and pay in no wise depend on the other man. What either does will not affect the other's task or rates."[75] Furthermore, in some industries it is difficult under a system of payment by result to arrange that the actual wages received by the average members of the group for average effort, will be approximately equal. Those are the industries in which there are a great variety of jobs with different rates, which can only be more or less accurately estimated in the "price list"; or industries in which the working conditions vary greatly, either within the same factory or mine, or between different factories or mines engaged in similar work.