A report by Goldman Sachs Group Inc. found that in 2017 and 2018, the biggest newly public companies would have had higher market values if they stayed private.

In the last 25 years, this dynamic only appeared in 2006 to 2007, before the financial crisis, and in 1998 to 2000, before the Tech Bubble, according to Goldman Sachs analysts.

On an absolute basis over the last five years, annualized private market gains for private companies was 33% higher than the gains of public companies. For Goldman Sachs, this means that value creation has recently shifted in favor of private markets.

The top 20 unicorns, privately held startups valued at over $1 billion, are about one year older than the average company age at IPO, which supports the idea that private companies are waiting longer before going public, the analysts said. With present record fundraising levels for venture capital, higher valuations of unicorns will continue.

The report also noted that the largest IPOs since 2015 were the biggest underperformers since 1998 to 2000. IPOs over the last six years have grown by only 50%, versus the median public market value creation of 151%.

Future IPOs may mitigate the trend favoring private companies, according to Goldman Sachs analysts. They added that they expect more unicorns in 2019, citing the current fundraising in large venture capitals.