The article explores how companies in different markets can form groups to control prices. They found that when production costs don't increase too much with quality, cartels tend to push lower quality products out of the market. However, if costs rise a lot with quality, all product types can still compete. Different sizes of cartels can form, but only industry-wide cartels are strong enough to resist members breaking away. This suggests that companies have a big reason to work together on pricing when they sell products with different quality levels.