Reading 31 Evaluating Portfolio Performance Flashcards
Three questions naturally arise in examining the investment performance of an account
Three questions naturally arise in examining the investment performance of an account:
- What was the account’s performance?
- Why did the account produce the observed performance?
- Is the account’s performance due to luck or skill?
The first issue is addressed by performance measurement, which calculates rates of return based on investment-related changes in an account’s value over specified time periods. Performance attribution deals with the second issue. It extends the results of performance measurement to investigate both the sources of the account’s performance relative to a specific investment benchmark and the importance of those sources. Finally, performance appraisal tackles the third question. It attempts to draw conclusions concerning the quality (that is, the magnitude and consistency) of the account’s relative performance.
Performance measurement
Performance measurement is a component of performance evaluation. Performance measurement is the relatively simple procedure of calculating returns for an account. Performance evaluation, on the other hand, encompasses the broader and much more complex task of placing those investment results in the context of the account’s investment objectives.
Performance measurement is the first step in the performance evaluation process. Yet it is a critical step, because to be of value, performance evaluation requires accurate and timely rate-of-return information. Therefore, we must fully understand how to compute an account’s returns before advancing to more involved performance evaluation issues.
Performance appraisal involves interpretation of performance attribution.
The emphasis on income-related return measures was due what factors?
Performance was typically measured on an income-only basis, thus excluding the impact of capital appreciation. For example, current yield (income-to-price) and yield-to-maturity were commonly quoted return measures.
The emphasis on income-related return measures was due to several factors:
- Portfolio management emphasis on fixed-income assets. Particularly in the low-volatility interest rate environment that existed prior to the late 1970s, bond prices tended to be stable. Generally high allocations to fixed-income assets made income the primary source of investment-related wealth production for many investors.
- Limited computing power. Accurately accounting for external cash flows when calculating rates of return that include capital appreciation requires the use of computers. Access to the necessary computing resources was not readily available. The income-related return measures were simpler and could be performed by hand.
- Less competitive investment environment. Investors, as a whole, were less sophisticated and less demanding of accurate performance measures.
The time-weighted rate of return (TWR)
The time-weighted rate of return (TWR) reflects the compound rate of growth over a stated evaluation period of one unit of money initially invested in the account. Its calculation requires that the account be valued every time an external cash flow occurs.
The subperiod returns can be combined through a process called chain-linking. Chain-linking involves first adding 1 to the (decimal) rate of return for each subperiod to create a set of wealth relatives. A wealth relative can be thought of as the ending value of one unit of money (for example, one dollar) invested at each subperiod’s rate of return. Next, the wealth relatives are multiplied together to produce a cumulative wealth relative for the full period, and 1 is subtracted from the result to obtain the TWR.
The money-weighted rate of return (MWR)
The money-weighted rate of return (MWR) measures the compound growth rate in the value of all funds invested in the account over the evaluation period. In the corporate finance literature, the MWR goes by the name internal rate of return, or IRR. Of importance for performance measurement, the MWR is the growth rate that will link the ending value of the account to its beginning value plus all intermediate cash flows. With MV1 and MV0 the values of the account at the end and beginning of the evaluation period, respectively, in equation form the MWR is the growth rate R that solves
MV1 = MV0(1 + R)m + CF1(1 + R)m–L(1) + … + CFn(1 + R)m–L(n)
where
m = number of time units in the evaluation period (for example, the number of days in the month)
CFi = the ith cash flow
L(i) = number of time units by which the ith cash flow is separated from the beginning of the evaluation period
TWR versus MWR
- The MWR represents the average growth rate of all money invested in an account, while the TWR represents the growth of a single unit of money invested in the account. Consequently, the MWR is sensitive to the size and timing of external cash flows to and from the account, while the TWR is unaffected by these flows. Under “normal” conditions, these two return measures will produce similar results.
- When external cash flows occur that are large relative to the account’s value and the account’s performance is fluctuating significantly during the measurement period, then the MWR and the TWR can differ materially.
- If funds are contributed to an account prior to a period of strong performance, then the MWR will be positively affected compared to the TWR, as a relatively large sum is invested at a high growth rate.
- Conversely, if funds are withdrawn from the account prior to the strong performance, then the MWR will be adversely affected relative to the TWR. (The opposite conclusions hold if the external cash flow occurred prior to a period of weak performance.)
- The TWR is unaffected by external cash flow activity. Valuing the account at the time of each external cash flow effectively removes the impact of those flows on the TWR. Consequently, the TWR accurately reflects how an investor would have fared over the evaluation period if he or she had placed funds in the account at the beginning of the period.
- In most situations, an investment manager has little or no control over the size and timing of external cash flows into or out of his or her accounts. Therefore, practitioners generally prefer a rate-of-return measure that is not sensitive to cash flows if they want to evaluate how a manager’s investment actions have affected an account’s value.
The Linked Internal Rate of Return (LIRR)
- Despite its useful characteristics, the TWR does have an important disadvantage: It requires account valuations on every date that an external cash flow takes place. Thus, calculation of the TWR typically necessitates the ability to price a portfolio of securities on a daily basis.
- The MWR, on the other hand, despite its sensitivity to the size and timing of external cash flows, requires only that an account be valued at the beginning and end of the evaluation period and that the amounts and dates of any external cash flows be recorded.
- The complementary advantages and disadvantages of the TWR and the MWR led to make an important recommendation: The TWR should be approximated by calculating the MWR over reasonably frequent time intervals and then chain-linking those returns over the entire evaluation period. This process is referred to as the Linked Internal Rate of Return (LIRR) method.
- The study concluded that only under unusual circumstances would the LIRR fail to provide an acceptable representation of the TWR. Specifically, the LIRR would fail if both large external cash flows (generally over 10% of the account’s value) and volatile swings in subperiod performance occurred during the evaluation period. With an evaluation period as short as one month, the chances of such a joint event occurring for an account are low.
Annualized Return
In general, with measurement periods shorter than a full year, it is inadvisable to calculate annualized returns. Essentially, the person calculating returns is extrapolating the account’s returns over a sample period to the full year. Particularly for equity accounts, returns can fluctuate significantly during the remaining time in the evaluation period, making the annualized return a potentially unrealistic estimate of the account’s actual return over the full year.
Matrix pricing
Many thinly traded fixed-income securities, a current market price may not always be available. In that case, estimated prices may be derived based on dealer-quoted prices for securities with similar attributes (for example, a security with a similar credit rating, maturity, and economic sector). This approach is referred to as matrix pricing.
Properties of a Valid Benchmark
A valid benchmark is:
- Specified in advance. The benchmark is specified prior to the start of an evaluation period and known to all interested parties.
- Owned. The investment manager should be aware of and accept accountability for the constituents and performance of the benchmark. It is encouraged that the benchmark be embedded in and integral to the investment process and procedures of the investment manager.
- Measurable. The benchmark’s return is readily calculable on a reasonably frequent basis.
- Unambiguous. The identities and weights of securities or factor exposures constituting the benchmark are clearly defined.
- Reflective of current investment opinions. The manager has current investment knowledge (be it positive, negative, or neutral) of the securities or factor exposures within the benchmark.
- Appropriate. The benchmark is consistent with the manager’s investment style or area of expertise.
- Investable. It is possible to forgo active management and simply hold the benchmark.
Seven primary types of benchmarks
There are seven primary types of benchmarks in use.
- Absolute
- Manager Universes
- Broad Market Indexes
- Style Indexes
- Factor-Model-Based
- Returns-Based
- Custom Security-Based
Manager Universes Benchmark
Consultants and fund sponsors frequently use the median manager or fund from a broad universe of managers or funds as a performance evaluation benchmark. A median manager benchmark fails all the tests of benchmark validity except for being measurable.
Broad Market Indexes Benchmark
- Market indexes are well recognized, easy to understand, and widely available, and satisfy several properties of valid benchmarks. They are unambiguous, generally investable, and measurable, and they may be specified in advance.
- In certain situations, market indexes are perfectly acceptable as benchmarks, particularly as benchmarks for asset category performance or for “core” type investment approaches in which the manager selects from a universe of securities similar in composition to the benchmark.
- However, in other circumstances, the manager’s style may deviate considerably from the style reflected in a market index. For example, assigning a micro-capitalization US growth stock manager an S&P 500 benchmark clearly violates the appropriateness criterion.
Style Indexes Becnhmark
- Broad market indexes have been increasingly partitioned to create investment style indexes that represent specific portions of an asset category: for example, subgroups within the US common stock asset category. Four popular US common stock style indexes are 1) large-capitalization growth, 2) large-capitalization value, 3) small-capitalization growth, and 4) small-capitalization value.
- Similar to broad market indexes, investment style indexes are often well known, easy to understand, and widely available. However, their ability to pass tests of benchmark validity can be problematic. Some style indexes contain weightings in certain securities and economic sectors that are much larger than what many managers consider prudent. Further, the definition of investment style implied in the benchmark may be ambiguous or inconsistent with the investment process of the manager being evaluated.
- Users of style indexes should closely examine how the indexes are constructed and assess their applicability to specific managers.
Factor-Model-Based Benchmark
The simplest form of factor model is a one-factor model, such as the familiar market model. In that relationship, the return on a security, or a portfolio of securities, is expressed as a linear function of the return on a broad market index, established over a suitably long period (for example, 60 months):
Rp = ap + βpRI + εp
These benchmarks are not always intuitive to the fund sponsor and particularly to the investment managers (who rarely think in terms of factor exposures when designing investment strategies), are not always easy to obtain, and are potentially expensive to use. In addition, they are ambiguous. We can build multiple benchmarks with the same factor exposures, but each benchmark can earn different returns. For example, we can construct two different portfolios, each with a beta of 1.2 (“normal beta”), but the portfolios can have materially different returns. Also, because the composition of a factor-based benchmark is not specified with respect to the constituent securities and their weights, we cannot verify all the validity criteria (the benchmark may not be investable, for example).
Returns-Based Benchmark
These benchmarks are constructed using:
1) the series of a manager’s account returns (ideally, monthly returns going back in time as long as the investment process has been in place) and
2) the series of returns on several investment style indexes over the same period.
These return series are then submitted to an allocation algorithm that solves for the combination of investment style indexes that most closely tracks the account’s returns.
Returns-based benchmarks are generally easy to use and are intuitively appealing. They satisfy most benchmark validity criteria, including those of being unambiguous, measurable, investable, and specified in advance. Returns-based benchmarks are particularly useful in situations where the only information available is account returns. One disadvantage of returns-based benchmarks is that, like the style indexes that underlie the benchmarks, they may hold positions in securities and economic sectors that a manager might find unacceptable. Further, they require many months of observation to establish a statistically reliable pattern of style exposures. In the case of managers who rotate among style exposures, such a pattern may be impossible to discern.
Custom Security-Based Benchmark
- A custom security-based benchmark is simply a manager’s research universe weighted in a particular fashion. Most managers do not use a security weighting scheme that is exactly an equal weighting across all securities or one that exactly assigns weights according to market capitalization. Consequently, a custom benchmark reflecting a particular manager’s unique weighting approach can be more suitable than a published index for a fair and accurate appraisal of that manager’s performance.
- The overwhelming advantage of a custom security-based benchmark is that it meets all of the required benchmark properties and satisfies all of the benchmark validity criteria, making it arguably the most appropriate benchmark for performance evaluation purposes. In addition, it is a valuable tool for managers to monitor and control their investment processes and for fund sponsors to effectively allocate or budget risk across teams of investment managers.
- One major disadvantage is that custom security-based benchmarks are expensive to construct and maintain. In addition, as they are not composed of published indexes, the perception of a lack of transparency can be of concern.
- In a custom-security-based benchmark, ther will be and should be misfit risk if the manager
s style is different than the broad market and if the custom benchmark accurately reflects the manager
s style.
The three steps reuired to construct a custom-security benchmark are as follows:
- Identify the manager’s investment process including asset selection and weighting
- Use the same assets and weighting for the benchmark
- Assess and rebalance the benchmark on a predetermined schedule
Building Custom Security-Based Benchmarks
The construction of such a benchmark involves the following steps:
- Identify prominent aspects of the manager’s investment process.
- Select securities consistent with that investment process.
- Devise a weighting scheme for the benchmark securities, including a cash position.
- Review the preliminary benchmark and make modifications.
- Rebalance the benchmark portfolio on a predetermined schedule.
Critique of Manager Universes as Benchmarks
- With the exception of being measurable, the median account in a typical commercially available universe does not have the properties of a valid benchmark.
- One of the most significant deficiencies is that, although the universe can be named, the median account cannot be specified in advance. Universe compilers can only establish the median account on an ex post basis, after the returns earned by all accounts have been calculated and ranked. Prior to the start of an evaluation period, neither the manager nor the fund sponsor has any knowledge of who the median manager will be at period end.
- In addition, different accounts will fall at the median from one evaluation period to another. For these reasons, the benchmark is not investable and cannot serve as a passive alternative to holding the account that is under analysis.
- Even after the evaluation period concludes, the identity of the median manager typically remains unknown, preventing the benchmark from satisfying the unambiguous property. The ambiguity of the median manager benchmark makes it impossible to verify its appropriateness by examining whether the investment style it represents adequately corresponds to the account being evaluated.
- Because fund sponsors terminate underperforming managers, universes are unavoidably subject to “survivor bias.”
- Placing above the median of a universe of investment managers or funds may be a reasonable investment objective, but the performance of a particular manager or fund is not a suitable performance benchmark that can be used to assess investment skill.
Set of benchmark quality criteria
Systematic Biases
Over time, there should be minimal systematic biases or risks in the benchmark relative to the account. One way to measure this criterion is to calculate the historical beta of the account relative to the benchmark; on average, it should be close to 1.0.
Tracking Error
We define tracking error as the volatility of A or (P – B). A good benchmark should reduce the “noise” in the performance evaluation process. Thus, the volatility (standard deviation) of an account’s returns relative to a good benchmark should be less than the volatility of the account’s returns versus a market index or other alternative benchmarks.
Risk Characteristics
An account’s exposure to systematic sources of risk should be similar to those of the benchmark over time. The objective of a good benchmark is to reflect but not to replicate the manager’s investment process. Because an active manager is constantly making bets against the benchmark, a good benchmark will exhibit risk exposures at times greater than those of the managed portfolio and at times smaller. Nevertheless, if the account’s risk characteristics are always greater or always smaller than those of the benchmark, a systematic bias exists.
Coverage
Benchmark coverage is defined as the proportion of a portfolio’s market value that is contained in the benchmark. For example, at a point in time, all of the securities and their respective weights that are contained in the account and the benchmark can be examined. The market value of the jointly held securities as a percentage of the total market value of the portfolio is termed the coverage ratio. High coverage indicates a strong correspondence between the manager’s universe of potential securities and the benchmark. Low coverage indicates that the benchmark has little relationship, on a security level, with the opportunity set generated by the manager’s investment process.
Turnover
Benchmark turnover is the proportion of the benchmark’s market value allocated to purchases during a periodic rebalancing of the benchmark. Because the benchmark should be an investable alternative to holding the manager’s actual portfolio, the benchmark turnover should not be so excessive as to preclude the successful implementation of a passively managed portfolio.
Positive Active Positions
An active position is an account’s allocation to a security minus the corresponding weight of the same security in the benchmark. When a good custom security-based benchmark has been built, the manager should be expected to hold largely positive active positions for actively managed long-only accounts.
Note that when an account is benchmarked to a published index containing securities for which a long-only manager has no investment opinion and which the manager does not own, negative active positions will arise. A high proportion of negative active positions is indicative of a benchmark that is poorly representative of the manager’s investment approach.
Hedge Funds and Hedge Fund Benchmarks
- Hedge funds attempt to expose investors to a particular investment opportunity while minimizing (or hedging) other investment risks that could impact the outcome. In most cases, hedging involves both long and short investment positions.
- The ambiguity of hedge fund manager opportunity sets has led to the widespread use of the Sharpe ratio to evaluate hedge fund manager performance.
- Typically, a hedge fund’s Sharpe ratio is compared to that of a universe of other hedge funds that have investment mandates assumed to resemble those of the hedge fund under evaluation. Unfortunately, this approach is exposed to the same benchmark validity criticisms leveled against standard manager universe comparisons. Further, the standard deviation as a measure of risk (the denominator of the Sharpe ratio) is questionable when an investment strategy incorporates a high degree of optionality (skewness), as is the case for the strategies of many hedge funds.
- Problems with using traditional techniques to assess long-short hedge funds include:
- It is possible for MV0 (market value at the beginning of the period) to be zero for a long-short portfolio, making the return calculation nonsensical.
- Many hedge funds use “absolute return” approach, which makes relative performance comparison with a traditional benchmark less useful.
- Alternative performance methods that can be used instead:
- Value-added return
- Creating separate long/short benchmarks
- the Sharpe ratio
Impact Equals Weight Times Return
A manager can have a positive impact on an account’s return relative to a benchmark through two basic avenues:
1) selecting superior (or avoiding inferior) performing assets and
2) owning the superior (inferior) performing assets in greater (lesser) proportions than are held in the benchmark.
This simple concept underlies all types of performance attribution. The assets themselves may be divided or combined into all sorts of categories, be they economic sectors, financial factors, or investment strategies. In the end, however, the fundamental rule prevails that impact equals (active) weight times return.