Andrew Wiechmann
Analyst · Morgan Stanley
Thanks, Baer, and hello to everyone on the call this morning. As Henry and Baer noted, we finished 2020 with a strong fourth quarter and significant momentum heading into 2021.
In Index, we recorded double-digit subscription run rate growth for the 28th consecutive quarter. Market cap weighted modules, which represent the largest part of our index subscription run rate, continued to deliver strong growth of approximately 9% in the quarter; while our factor, ESG, custom and specialized modules grew at healthy double-digit growth rates.
From a client segment perspective, the index subscription run rate growth with asset managers, the largest client segment, was 9%; while growth rates among wealth managers, hedge funds and asset owners were all greater than 15%. Assets under management and equity ETFs linked to MSCI indexes reached record levels, driven by strong cash inflows of $59 billion or close to 30% of all cash inflows into equity ETFs during the quarter. This was driven by strong market share capture of cash inflows across all geographic regions and particular strength in emerging market exposures.
Equity ETFs linked to MSCI ESG and climate indexes experienced cash inflows of nearly $25 billion during the quarter. These cash inflows represented nearly 80% of all inflows into ESG and climate ETFS. Overall, asset-based fee revenue was up over 15% year-on-year, reflecting higher results across the board, including from ETFs, non-ETF passive products and futures and options.
Turning now to our adjusted earnings per share growth year-over-year. Underlying business performance drove the vast majority of our growth in adjusted EPS, while our share repurchases also contributed. Operating revenue growth was strong, and year-over-year expenses were up modestly, once again, benefiting from lower travel and entertainment expenses, which were lower than the fourth quarter of 2019 by $4.2 million and somewhat offset by our reaccelerated pace of investments in the second half of 2020.
Turning to our balance sheet. We continue to have strong liquidity that provides us tremendous flexibility. We finished the quarter with total debt to adjusted EBITDA of 3.5x, at the top end of our targeted range of 3 to 3.5x. Lower cash tax payments and disciplined client collections led to significant outperformance in our free cash flow generation in the fourth quarter relative to our guidance.
As Henry noted earlier, we have been pleased with the success of our capital management strategy, and we'll continue our disciplined and patient approach to allocating capital. We are keenly focused on reinvesting in the business as a first priority, optimizing our leverage profile to enhance returns and maintain flexibility, providing a consistent quarterly dividend that grows with earnings and is based on a payout ratio of 40% to 50% of adjusted EPS, opportunistically pursuing MP&A and share repurchases with an intense focus on maximizing returns to shareholders and preserving a strong liquidity position.
As Henry noted, to enhance shareholder awareness and understanding of our progress in pursuing key growth opportunities in ESG and climate and in private assets, starting this year, we will present ESG and climate as its own reporting segments and All Other will consist of operating segments and private assets. Beginning in April, when we report Q1 earnings, you will see the same financial and operating metrics we currently show for the Index and Analytics segments also for the ESG and Climate segment and for Real Estate. So that you have historical information for comparative purposes, we will provide information for the new reporting segment annually for 2018 and 2019 and quarterly for 2020. Revenue and operating metrics from ESG and Climate indexes will remain within our Index segment. We are excited to bring this incremental transparency to our disclosures and to continue to update you on these exciting areas of growth and opportunity.
Before I turn to guidance, I would like to highlight that recurring subscription revenue has lagged subscription run rate by a slightly larger amount in the last couple of quarters. As noted in our disclosures, there are several factors that can contribute to this, including, but not limited to, the timing of sales and cancels; modifications; FX movements; delayed contract start dates, also known as advanced bookings; and implementation periods.
In response to the COVID pandemic, we have selectively used advanced bookings recently to help drive new business in key areas. When these are offered, the client is contractually committed to a subscription agreement, but may have access to the service prior to the beginning of the fee period at no cost. In these cases, the sale may be recognized before we begin recognizing revenue or we may recognize a lower amount of revenue in the first year relative to the size of the sale. We used these tools selectively this past year. And while we do intend to continue to use them going forward, we don't expect the magnitude to increase materially. However, as we said at the top of the call, we would caution you not to place undue reliance on run rate to estimate or forecast recurring revenues.
Turning to our guidance. Our expectations for 2021 reflect what we believe will be another strong year for MSCI with several guiding principles. Our expense guidance assumes relatively flat equity market levels for the year. As such, our expenses may flex up and down depending on market conditions and the trajectory of our asset-based fees. To that end, we will continue to implement our upturn and downturn playbooks if and when they are needed. As we've noted throughout this call, investing in our business remains our top priority. However, we are also committed to delivering positive operating leverage, although you should expect to see more modest margin expansion than in recent past.
Our free cash flow guidance reflects strong operating performance and strong collections; relatively flat market levels, although we could, of course, see markets perform better or worse; margin expansion over the course of the year, again, likely at a more modest pace than in recent past; and higher cash taxes in 2021.
In summary, 2020 was a very strong year for MSCI despite the global hardship related to the pandemic. We have continued to deliver innovative indexes, research, data and other tools. We've executed against our strategic priorities, staying incredibly productive and engaged as a team. And as always, we remain committed to driving further value for our shareholders. We look forward to speaking with you in a few weeks at Investor Day.
And with that, operator, please open the line for questions.