In an ascending-bid auction, the price starts at a low level and gradually increases as bidders compete by submitting higher bids until a winner is determined.

First-price auction is not a common type of auction. In a first-price auction, the highest bidder wins the item and pays the amount of their bid, while in a second-price auction, the highest bidder wins the item but pays the amount of the second-highest bid.

In a sealed-bid auction, bidders submit their bids simultaneously and independently, without knowing the bids of other participants.

In a second-price auction, the Nash equilibrium is for each bidder to bid their true valuation of the item. This is because bidding above their true valuation increases the chance of winning but also increases the amount they have to pay if they win, while bidding below their true valuation decreases the chance of winning.

Natural experiments are not commonly used in auction research because they rely on naturally occurring events that cannot be controlled by the researcher.

In Kagel and Levin's (2002) experiment, the number of bidders was variable, ranging from 2 to 6, to study how the number of bidders affects auction outcomes.

Experimental studies have not consistently shown that bidders are more likely to collude in sealed-bid auctions compared to ascending-bid auctions.

In Cox, Smith, and Walker's (1988) experiment, the value of the item was known to some bidders but not others to study how asymmetric information affects auction outcomes.

Experimental methods do not necessarily provide a more realistic setting compared to theoretical models. In fact, experiments are often conducted in controlled environments that may not fully capture the complexity of real-world auctions.

In Harrison, Kagel, and Vinokur's (1990) experiment, both human beings and computers participated in auctions to study how human behavior differs from computer-generated bidding strategies.

Sequential auctions are not commonly used in experimental research because they are more complex to conduct and analyze compared to other types of auctions.

In Gneezy and Rustichini's (2000) experiment, both students and businesspeople participated in auctions to study how different demographic groups behave in auctions.

Experimental studies have not consistently shown that bidders with more information are more likely to collude.

In Kagel and Levin's (2010) experiment, subjects from different countries and cultures participated in auctions to study how cultural differences affect auction outcomes.

The ability to control the environment and isolate specific factors is a strength, not a limitation, of experimental methods.