Big banks and software companies are among the most exposed to "key man" risk, according to a recent note from Morgan Stanley. Morgan Stanley looked at the risks of having a hugely important executive such as a CEO or chairman, dubbed a key man, suddenly step down. The bank found a rise in key-man turnover in recent years. Fifty-nine CEOs in the S&P 500 left their companies in 2017, and new data suggests an 11% increase year-on-year for key-man departures in the first half of 2018. PepsiCo CEO Indra Nooyi is the latest top executive to go, resigning Monday after 12 years in the role. Companies with key-man losses in 2017 underperformed the rest of the market by 11% on average over the next 12 months, with 32% of those companies underperforming the rest of the market by more than 20%, according to the research. Key men are defined as executives who may be a company's founder, and therefore likely more integral to its value; are thought leaders in their industry; have key strategic knowledge and importance; or have a proven track record of value creation. One in four large-cap banks have a key-man risk, according to Morgan Stanley's analysis. The most notable is JPMorgan. CEO Jamie Dimon was appointed in 2005 and has presided over a stock-price increase of 193% after steering the bank through the financial crisis. Dimon has achieved annual returns of more than 200 basis points above the S&P 500 during his tenure and has guided the bank to a greater scale and share value. He said in February that he planned to stay on as CEO and chairman for another five years. Morgan Stanley questions whether Dimon's successor will be capable of generating the same leadership and results. "Successors are viewed to be co-Presidents Gordon Smith and Daniel Pinto, Head of Asset Management Mary Erdoes, and CFO Marianne Lake," Morgan Stanley's analysts wrote. "Investor question is can these potential successors deliver the profitable growth that Dimon has executed across JPM's unmatched breadth of product and geography." Morgan Stanley recommends investors become aware of the risks by asking questions about planned corporate succession, diversity of value held by senior leadership staff around the CEO, and learning more about the specific role a CEO plays in leading their company.