### Abstract

In this tutorial, we monitor the news sentiment for the constituents of 25 different sector Exchange Traded Funds (ETFs). We periodically rebalance the portfolio of ETFs to maximize our exposure to the sectors with the greatest public sentiment. The results show that the strategy consistently outperforms several benchmark approaches.

### Background

Sector rotation is a strategy where you move capital among a set of sectors in an effort to outperform the overall market. Each market sector has an environment in which it performs best. Therefore, by increasing your exposure to the best performing sectors and decreasing your exposure to the worst performing sectors, you can concentrate your portfolio in the sectors that are favorable to the current market environment.

### Method

Let’s examine how we can implement a sector rotation strategy based on news sentiment with the LEAN algorithmic trading engine and datasets from the QuantConnect Dataset Market.

#### Universe Selection

This algorithm requires three universes.

First, we need a static universe of the sector ETFs. To avoid selection bias, we use all of the 25 sector ETFs from the CNBC website.

var tickers = new[]
{
"XLE", // Energy Select Sector SPDR Fund
"XLF", // Financial Select Sector SPDR Fund
"XLU", // Utilities Select Sector SPDR Fund
"XLI", // Industrial Select Sector SPDR Fund
"GDX", // VanEck Gold Miners ETF
"XLK", // Technology Select Sector SPDR Fund
"XLV", // Health Care Select Sector SPDR Fund
"XLY", // Consumer Discretionary Select Sector SPDR Fund
"XLP", // Consumer Staples Select Sector SPDR Fund
"XLB", // Materials Select Sector SPDR Fund
"XOP", // Spdr S&P Oil & Gas Exploration & Production Etf
"IYR", // iShares U.S. Real Estate ETF
"XHB", // Spdr S&P Homebuilders Etf
"ITB", // iShares U.S. Home Construction ETF
"VNQ", // Vanguard Real Estate Index Fund ETF Shares
"GDXJ",// VanEck Junior Gold Miners ETF
"IYE", // iShares U.S. Energy ETF
"OIH", // VanEck Oil Services ETF
"XME", // SPDR S&P Metals & Mining ETF
"XRT", // Spdr S&P Retail Etf
"SMH", // VanEck Semiconductor ETF
"IBB", // iShares Biotechnology ETF
"KBE", // SPDR S&P Bank ETF
"KRE", // SPDR S&P Regional Banking ETF
"XTL"  // SPDR S&P Telecom ETF
};

foreach (var ticker in tickers)
{
// …
}


Second, we need an ETF Constituents universe so we can get the dynamic constituents of each sector ETF.

foreach (var ticker in tickers)
{
constituents =>
{
_etfConstituentsDataBySymbol[etfSymbol] = constituents;
return Enumerable.Empty<Symbol>();
})
);
}


Third, we need a BrainSentimentIndicatorUniverse so we can get the Brain Sentiment Indicator values of the constituents in each market sector.

AddUniverse<BrainSentimentIndicatorUniverse>(
"BrainSentimentIndicatorUniverse", Resolution.Daily,
altCoarse =>
{
_brainUniverseData = altCoarse.ToList();
return Enumerable.Empty<Symbol>();
});


#### Scheduling Rebalances

We set a Scheduled Event to trigger monthly rebalances. To test how sensitive the algorithm’s performance is to the rebalancing date, we use a parameter to test rebalancing the portfolio on the 1st, 5th, and 12th trading day of each month.

Schedule.On(DateRules.MonthStart(GetParameter("rebalance-day", 0)),
TimeRules.Midnight,
() =>
{
_rebalance = true;
});


#### Calculating Sector Sentiment

We utilize the Brain Sentiment Indicator dataset to calculate the sentiment of each sector. The indicator values are created by analyzing financial news using Natural Language Processing techniques while taking into account the similarity and repetition of news on the same topic. The sentiment score assigned to each stock ranges from -1 (most negative) to +1 (most positive). The 30-day sentiment score of a security corresponds to the average sentiment for each piece of news for the security over the last 30 days.

During each rebalance, we calculate the sentiment of each sector through the following procedure:

1. Select a sector ETF.
2. Select the ETF constituents that have Brain Sentiment Indicator data.
3. Multiply the Brain Sentiment over the last 30 days by the ETF weight of each constituent.
4. Sum up the set of products from the previous step.
foreach (var kvp in _etfConstituentsDataBySymbol)
{
var etfSymbol = kvp.Key;
var etfConstituentsData = kvp.Value;
var sectorSymbols = etfConstituentsData.Select(etfConstituentsData => etfConstituentsData.Symbol).ToHashSet();
var etfWeightBySymbol = sectorSymbols.ToDictionary(
sectorSymbol => sectorSymbol,
sectorSymbol => etfConstituentsData.Where(etfConstituentsData => etfConstituentsData.Symbol == sectorSymbol).FirstOrDefault().Weight
);

_scoreBySector[etfSymbol] = _brainUniverseData
.Where(brainSentiment => sectorSymbols.Contains(brainSentiment.Symbol))
.Select(brainSentiment => brainSentiment.Sentiment30Days * etfWeightBySymbol[brainSentiment.Symbol])
.Sum();
}


#### Rotating Between Sectors

After determining the sentiment of each sector, we select the three sectors with the greatest news sentiment and place orders to allocate ⅓ of our capital to the three corresponding sector ETFs.

// Select target ETFs
var targetSymbols = _scoreBySector.OrderByDescending(x => x.Value)
.Take(_numEtfs)
.Select(kvp => kvp.Key);

// Liquidate ETFs that are no longer targeted
SetHoldings(Portfolio.Where(kvp => kvp.Value.Invested && !targetSymbols.Contains(kvp.Key))
.Select(kvp => new PortfolioTarget(kvp.Key, 0))
.ToList());

// Rebalance targeted ETFs
var weight = 1.0m / _numEtfs;
SetHoldings(targetSymbols.Select(symbol => new PortfolioTarget(symbol, weight)).ToList());


### Results

We backtested several versions of the strategy from January 1, 2017 to November 1, 2022. The following image displays the equity curves of each version of the strategy and each version of the benchmark when we rebalance the portfolio on the first trading day of each month.

The following table summarizes each version of the algorithm and shows its resulting Sharpe ratio. To reproduce our results, clone and backtest each algorithm.

Algorithm Sharpe Ratio Description
Benchmark - SPY 0.564 Allocate 100% of the portfolio to the S&P 500 Index ETF.
Benchmark - Equal Weighting 0.436 During each rebalance, allocate an equal portion of the portfolio to each sector ETF.
Benchmark - Momentum 0.336 During each rebalance, allocate an equal portfolio of the portfolio to the $n$ (3) sector ETFs that had the greatest return over the last month.
Strategy - Simple Average 0.59 Calculate the sector sentiment by taking the average sentiment of all the ETF constituents. During each rebalance, allocate an equal portion of the portfolio to the top $n$ (3) sector ETFs.
Strategy - Simple Average of Top Performers 0.697 Calculate the sector sentiment by taking the average sentiment of the $x$% (50%) of ETF constituents with the largest weight in the ETF. During each rebalance, allocate an equal portion of the portfolio to the top $n$ (3) sector ETFs.

This technique lets us diverge from the ETF and only trade constituents that matter.
Strategy - Weighted Average 0.806 Calculate the sector sentiment by taking the weighted average of all the ETF constituents. During each rebalance, allocate an equal portion of the portfolio to the top $n$ (3) sector ETFs.

This technique reflects the fact that the sentiment of large constituents has more impact on the sector performance.

The results show that each version of the strategy had greater risk-adjusted returns than all of the benchmarks.

Furthermore, the following table shows the Sharpe ratios of the weighted average strategy and the equal weighted benchmark for each rebalancing date:

Rebalancing Day Benchmark - Equal Weighting Strategy - Weighted Average
Std of Results 0.0026 0.0672

The results show the strategy had greater risk-adjusted returns than the benchmark for each rebalancing date, but the strategy’s performance was more sensitive to changes in the rebalancing date.

To determine if the strategy’s outperformance of the benchmark is statistically significant, we run a paired t-test on the difference between the daily returns of the strategy and each benchmark. The null hypothesis of this test is that the mean difference between the daily returns of the strategy and the benchmark is zero. The alternative hypothesis is that the mean difference is positive. The following table shows the p-values of the one-sided t-test with each benchmark and the strategy. The strategy in this case is the weighted average version when we rebalance it on the 12th trading day of each month.

Benchmark T-test P-value (%)
SPY 3.17
Equal Weighting 0.95
Momentum 1.03

All the t-tests produce a p-value less than 5%, so it lends support to the hypothesis that the mean difference between the daily returns of the strategy and each benchmark is above zero. To reproduce these p-value results and the preceding equity curve plot, backtest each algorithm, then run the notebook cells in this project.