Aggregate Attention∗

Aggregate attention Paul J. Irvine Neeley School of Business Texas Christian University June, 2021 Abstract We study some of the aggregate properties of investor attention to the stock market. We introduce a framework that constructs a null hypothesis of what rational aggregate attention should look like. This framework states that aggregate attention should be proportional to the aggregate wealth invested in each stock. We find that the distribution of attention at first appears rational. However, much of this attention is directed away from the high market cap names that should attract the most attention. Attention is notably more volatile from month to month than market cap, making attention unpredictable from a market maker perspective This pattern generates pricing errors that result in the most popular stocks performing poorly in the upcoming month. This poor performance appears to be a short-term reversal of pricing errors generated by the unpredictable liquidity demands volatile attention can generate. All errors are our own. Preliminary and incomplete. Thanks to David Rakowski, Joey Engelberg, Siyi Shen, and seminar participants at the University of South Carolina. Corresponding author: [email protected]. Aggregate Attention Abstract We study some of the aggregate properties of investor attention to the stock market. We introduce a framework that constructs a null hypothesis of what rational aggregate attention should look like. This framework states that aggregate attention should be proportional to the aggregate wealth invested in each stock. We find that the distribution of attention at first appears rational. However, much of this attention is directed away from the high market cap names that should attract the most attention. Attention is notably more volatile from month to month than market cap, making attention unpredictable from a market maker perspective This pattern generates pricing errors that result in the most popular stocks performing poorly in the upcoming month. This poor performance appears to be a short-term reversal of pricing errors generated by the unpredictable liquidity demands volatile attention can generate. 1 Introduction Attention is a scarce resource. How do investors allocate their attention across stocks? Do they allocate attention rationally? What constitutes a measure of rational attention? This paper intends to provide evidence on these questions. We use a large data set of investor posts from the website Stocktwits, to evaluate the distribution of attention across stocks. In addition, we evaluate how attention responds to stock returns, news articles, and other factors proposed in the literature to proxy for attention. The goal of this paper is to provide a broad set of facts on aggregate investor attention, that can hopefully guide the burgeoning literature on attention and its effects in financial economics. What should be the rational level of investor attention? It is almost tautological nowadays to assume that an individuals level of attention is limited, sometimes this bound is imposed by cognitive capability, in other settings by the restrictions of the effort required, or the limited time involved, sometimes by all of these factors. An early attempt to incorporate these limitations directly into the stock market is Merton (1987) who notes, quite correctly, that investors seem limited in the set of stocks they ‘know about’, and thus pay attention to. Casual observation leads to the obvious conclusion that different individual investors pay attention to different sets of stocks. So how should these distinct attention sets aggregate in the stock market? We propose a simple framework that assumes investors should aggregate attention in proportion to their wealth invested in different stocks. Fortunately, we know how wealth aggregates across stocks since we can easily calculate market capitalization weights. Therefore, we propose a null hypothesis that attention across investors should aggregate in proportion to a stock’smarket cap weight. We examine the aggregate properties of investor attention using data from the Stocktwits web site. Stocktwits is a site where investor can post short notes on individual stocks. These notes are aggregated into a thread that is continually updated as new investors post their notes or reactions to the market action, news reports, dividend news, or other posts. Stocktwits has grown considerably since its introduction in 2008, and currently has the 1 advantage of covering a large and broad set of investors and stocks. In using this data, we do assume that posting about a stock implies the investor is paying attention to the stock. This does not seem like an extreme assumption since to post an investor must identify the stock by ticker symbol, so clearly the attention is specific to that stock, and this attention is recorded when they take enough interest in the stock to write a post about it. In doing so, they are very likely follow the thread containing other posts on the same stock, thus applying their limited supply of attention to the posted stock. Existing papers using network data concentrate on the effects of abnormal attention on sentiment or stock returns. For example, Da, Engelberg and Gao (2011) use Google search intensity as a proxy for attention and show that interest in the ticker is related to IPO initial returns. Ben-Rephael, Da, and Israelsen (2017) use the Bloomberg news network to examine the effects of abnormal institutional attention on the speed of return responses to news events. Because of restrictions on the way Google search intensity and Bloomberg news are disseminated, they are problematical for measuring aggregate attention. Social networks are studied by Giannini, Irvine and Shu (2018) who relate social media sentiment to overpricing by physically distant investors. Rakowski, Shirley and Stark (2020) use Twitter outages to infer the effects of social media activity on volume and returns. As in Giannini et al. (2019), Rakowski et al. (2020) find that social media activity can be particularly revealing around earnings announcements. A number of more obscure attention and return studies have been performed in international settings, usually with Twitter since it has the most accessible API. These international studies produce mixed results; usually they report a relation between attention and returns, but it is not always a relation that is consistent with other findings (Yoshinaga and Rocco, 2020). Stocktwits data has proven to be particularly useful in Cookson and Neissner’s(2020) study of disagreement and investor type, in Giannini et al.’s (2019) study of investor disagreement around earnings announcements, as a data source to define political leanings in Cookson, Engelberg, and Mullins (2020), and in Cai, Yung, and Zhu’s(2019) study of sentiment and post-earnings announcement drift. 2 In his treatise on attention and effort, Kahneman (1973) discusses why individuals appear to selectivity attend some stimuli, in preference of others This selective attention is set in a framework where attention requires effort, a resource that is limited, and therefore must be distributed selectively. Most of the literature on attention in psychology has focused on what stimuli attract individual attention. In economics, a natural focus point is how limited attention affects consumer choice (De Clippel, Eliaz, and Rozen, 2014). However, Kahneman’s(1973) ideas of a capacity on attention are used in accounting and finance papers like Hirshleifer and Teoh (2003), Peng and Xiong (2006), DellaVigna and Pollet (2009), and Hirshleifer, Kim and Teoh (2009). In this paper, we focus on aggregate attention, or how the collective selective attention by individuals aggregates to a whole. In particular, we focus on attention to stocks, and how the attention of investors aggregates across stocks. Our first empirical tests examine the concentration of investor attention and compares the level of concentration in attention to the concentration of market value and volume. We represent concentration as a power law, where the exponent of the power law can be estimated empirically, and yields a compact way to describe concentration across a large set of stocks. Using a sample of 100 stocks, the initial indication is that attention is rational in that investors allocate their attention in the same way that market capitalization is allocated across stocks. However, when we expand the set of stock examined to 200, 500, or 1,000 stocks, we find that investor attention tends to be more and more concentrated than market capitalization. In fact, attention and trading volume tend to reflect a similar pattern, in that volume is more concentrated than market cap as well. This change in attention concentration as we expand the sample indicates that investor attention is rational relative to market cap, at least for the top 100 stocks, but investors are relatively inattentive as we go down the market cap scale. This finding provides behavioral support for the ‘neglected firm’effect, first proposed by Arbel and Strebel (1982). Some of the characteristics of aggregate attention can be important for models such as Hendershott, Menkveld, Praz and Seasholes (2021) who extend the slow moving capital 3 ideas of Bogousslavsky (2016) and Duffi e (2010) to explain mispricing and mean reversion in prices at different time scales. Their model relies on two groups of inattentive investors whose lack of attention drives episodic liquidity demands that can distort prices. Their model has little behavioral

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