How are two cobblers who control the shoe making business an oligopoly?

Two cobblers who control the shoe making business could be an oligopoly in a situation with the following conditions:

- a small number of firms (two or more) have full (or most) control of an industry

- options such as price and/or output amount depends on the other firm offering the service in the industry.

- barriers to entry enabling market share between the firms

- differentiated products/services including effective advertising and quality products/services.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.