When the same numbers of people move up and down the social class ladder but remain in proportion and balance this is referred to as which one of the following types of social mobility?

When the same numbers of people move up and down the social class ladder but remain in proportion and balance, this is referred to as structural social mobility. This type of mobility occurs due to changes in the economy or society that affect all social classes, rather than individual achievements. It highlights how shifts in the job market or societal structures can lead to simultaneous upward and downward movement among different groups, maintaining overall class proportions.