The study looks at how unions affect economic growth by bargaining for higher wages for low-skilled workers. This can lead to unemployment, which can be bad for growth. However, it also causes high-skilled workers to move from manufacturing to research, which can boost growth. The overall impact depends on how easily high-skilled and low-skilled workers can be substituted for each other. If they can't be easily replaced, the positive effect of high-skilled workers moving to research outweighs the negative impact of higher wages for low-skilled workers.