Gov. Corbett's decision Wednesday to forgo establishing a state-run health-insurance exchange under the Affordable Care Act means that Pennsylvania, along with New Jersey and 20 other states, will have an exchange run by the federal government.

Following are some questions and answers about the role that health-insurance exchanges will play and what the decisions by Corbett and Gov. Christie, who last Thursday decided to let the federal government run the New Jersey exchange, mean for residents of the two states:

Question: What are health-insurance exchanges?

Answer: They are online marketplaces where consumers and small businesses with up to 100 employees can view health-insurance options with benefits and costs in a standard format. The exchanges will also administer subsidies and automatically steer people to expanded Medicaid coverage if they are eligible.

Q. Who will use them?

A. The exchanges were conceived as a way to serve the uninsured, who will be required to buy insurance under health-care reform, and people who now buy individual insurance policies. Most who keep employer-based coverage will not use the exchange.

Q. How many residents of Pennsylvania and New Jersey are expected to get insurance on the exchanges?

A. It's too soon to say. New Jersey has 1.35 million uninsured, according to the Kaiser Family Foundation. In Pennsylvania, that number is 1.37 million. The pool of people with individual policies is smaller: 368,600 in New Jersey and 690,000 in Pennsylvania.

Q. When will the health insurance exchanges go into operation?

A. They are supposed to be open for enrollment on Oct. 1, and the insurance will be effective Jan. 1, 2014. Some critics have suggested that the federal government won't be ready.

Q. Why did the governors of New Jersey and Pennsylvania decide against state-run exchanges?

A. Like other Republican governors, they complained that there was too much uncertainty about how much it would cost to operate an exchange.

Q. What difference will it make to residents of Pennsylvania and New Jersey that the federal government will operate their exchanges?

A. Advocates for state-run exchanges said that by defaulting to the federal option, states give up the opportunity to customize the exchange for their markets. However, states have the option to adopt a state-run exchange later.