What can be concluded about the impact on stock values after the launch of companies on the American stock market?

The conclusion that some companies experience a decrease in value after launch is supported by a number of factors observed in stock market behavior. Historically, many companies that go public through an Initial Public Offering (IPO) can initially show increased enthusiasm and investment, but it is not uncommon for some of these stocks to decline in value shortly after their launch. This decrease can occur for various reasons, such as overvaluation at the time of launch, shifts in market sentiment, or disappointing financial performance following the IPO.

Several empirical studies also indicate a trend where not all IPOs result in sustained increases in stock price; while some companies may see their stock valuations rise, others may struggle or experience volatility, leading to subsequent declines. Market reactions can fluctuate based on broader economic conditions, investor perceptions, and specific news related to the company's performance or market competition. Therefore, the notion that a percentage of companies may decline in value post-launch aligns well with historical data and the unpredictability of market behavior.

The other options suggest absolute trends that do not reflect the complexity of the stock market, such as the idea that all companies either increase or decrease uniformly, or that market performance has no effect on company value, which does not account for the variable nature of investor reactions and economic factors.