Financial markets are essential in regulating economic development and promoting social progress. Different types of markets have different roles. The stock markets can reflect the development of a region’s economy, and are often called “the barometer” of the economy. Gold has scarcity and currency attributes, and it has vital strategic significance in economic development. It is often called “safe haven” for investors. Foreign exchange is not only an important part of a country’s international reserves, but is also an indispensable tool for international economic exchanges. Considering that different types of markets have different roles, stock, gold and foreign exchange respectively occupy crucial positions in the financial markets. A phenomenon known as “financial contagion” exists in financial markets. During the financial crisis, we often found that when a market suffered severe turbulence for the first time after the shock, this turbulence could spread to many other markets and countries as quickly as an “infectious disease” [
43]. As a result, the correlation between different markets or different assets at this time becomes much stronger than that in the quiet period. In other words, the distribution result of financial assets return show that the correlation is different at the tail of the distribution and at the middle of the distribution. Therefore, this paper analyzes the correlation difference of the three types of financial time series from the two viewpoints of time scale and quantile level, especially regarding the tail correlation.
6.1. Stock Market
It is useful to study the price dependence between stock markets in different regions, because the supply and demand relationship of the stock markets can be quickly reflected in prices. This paper selects the S&P 500 in the US, the HIS in China and the FTSE 100 in the UK as research objects. There are two reasons for choosing these stock indices. One is that these stock indices are important indices in the international stock markets, and the other is that these stock indices belong to different regions, respectively in the Americas, Asia and Europe. In this paper, the time scales are set to [1, 20], and the quantile levels are marked as [0.05, 0.95] (sampling interval is 0.05). Before applying the MQCC method, we first use the traditional correlation coefficient to test the correlation of the stock time series. The measurement results are shown in
Figure 5 below. The traditional correlation coefficient measurement results show that the correlation of the stock series is enhanced with the increase of the time scale. The S&P 500 and the FTSE 100 have the highest overall correlation. The correlation between the HIS and the FTSE 100 is stronger on the lower scale than the correlation between the HIS and the S&P 500. As the time scale increases, the correlation between the HIS and the FTSE 100 is not much different from the correlation between the HIS and the S&P 500. However, the results of the traditional correlation coefficient cannot reveal the strength of the tail correlation, and such a measurement is not accurate enough.
The MQCCs of the stock time series are shown in
Figure 6 below. From the three-dimensional figure, we can clearly see that the returns between these stock markets show a positive correlation, and the
-quantile correlation coefficient between the two markets increases with the increase of the time scale. At the level of raw data
, the quantile correlation coefficients of the returns of the HIS and the S&P 500 fluctuated between [0.20, 0.28], the quantile correlation coefficients of the HIS and the FTSE 100 fluctuated between [0.38, 0.47], and the quantile correlation coefficients of the S&P 500 and the FTSE 100 fluctuated between [0.55, 0.61]. From the whole trend, the correlation between the returns of the S&P 500 and the FTSE 100 was stronger than the correlation of the returns of the HIS and the FTSE 100. The correlation between the HIS and the S&P 500 was the lowest. On the lower time scales
, the quantile correlation coefficients of the returns of HIS and S&P 500, HIS and FTSE 100, and S&P 500 and FTSE 100 fluctuated respectively in the intervals [0.40, 0.72], [0.51, 0.75] and [0.64, 0.89]. On the medium time scales
, the correlation fluctuation ranges of the returns of the three stock indices changed to [0.50, 0.77], [0.44, 0.81] and [0.68, 0.94]. On the higher time scales
, there was not much difference from the middle time scales. The quantile correlation coefficients fluctuated within the intervals of [0.53, 0.87], [0.53, 0.86] and [0.68, 0.94]. Among them, the quantile correlation coefficients between two of three stock markets were higher when the time scale was set to around 14.
In addition, the quantile correlation coefficients of the time series of the two markets also differ significantly at different quantile levels. The positive correlation of the left tail is stronger than that of the right tail. In the left tail , the quantile correlation coefficients of the returns of the HIS and the S&P 500, the HIS and the FTSE 100, and the S&P 500 and FTSE 100 respectively fluctuated within the intervals of [0.26, 0.87], [0.45, 0.84] and [0.61, 0.94]. However, in the right tail , the quantile correlation coefficients of the corresponding stock markets fluctuated in the ranges [0.22, 0.71], [0.39, 0.70] and [0.55, 0.94], respectively. The strong correlation of the left tail may be explained by risk aversion in behavioral finance research. The attitude of most investors towards extreme returns is often unusual.
The difference and symmetry analysis results of the tail correlation among the returns of the stock markets are shown in
Figure 7 below. Judging from the tail correlation metric difference index
, compared with the 0.5 quantile correlation coefficient, the correlation difference between the left tail and the 0.5 quantile was greater than that of the right tail. Among the correlations between the HIS and the S&P 500, the HIS and the FTSE 100 and the S&P 500 and the FTSE 100, the correlation differences between the left tail and 0.5 quantiles fluctuated by [0.00, 0.19], [−0.02, 0.23] and [0.01, 0.17], respectively. However, the differences between the right tail and 0.5 quantiles fluctuated within [−0.16, 0.05], [−0.18, 0.12] and [−0.18, 0.10], respectively. The tail correlation symmetry measure
also reflects the obvious difference between the left and right tails’ correlation, and the tail correlations were asymmetric. Among them, the maximum difference between the left tail correlation and right tail correlation of the HIS and the S&P 500, the HIS and the FTSE 100 and the S&P 500 and the FTSE 100 were up to 0.28, 0.29 and 0.27, respectively.
In particular, we expect that the returns of financial assets will fluctuate sharply during the financial crisis, and the tail correlation between financial markets will be different from before. Our expectations are based on the theoretical and empirical financial literature, focusing on various findings [
23,
32,
44]. Using the 2008 financial crisis as the time node, this paper divides the original financial time series into two parts, before and after the financial crisis, and uses the quantile correlation coefficient to observe the correlation differences between the stock markets.
Figure 8 and
Figure 9 provide the tail correlation before and after the financial crisis.
On the whole, whether before the 2008 financial crisis or after the financial crisis, the returns of the S&P 500 and FTSE 100 showed the strongest positive correlation. The left tail correlation after the financial crisis is significantly higher than the left tail correlation before the financial crisis on different time scales, and the correlation of the left tail becomes stronger with the increase of the time scale. The right tail correlation after the financial crisis is also different. However, the correlation difference between the right tail before and after the financial crisis is not as obvious as the correlation difference between the left tail before and after. This shows that when facing extremely negative returns, the stock markets’ linkages in different regions are relatively strong. Tail symmetry was also found to be different. Before the financial crisis, the maximum differences between the left and right tails of the HIS and the S&P 500, the HIS and the FTSE 100 and the S&P 500 and the FTSE 100 were up to 0.31, 0.36 and 0.27, respectively. However, after the financial crisis, the maximum differences between the left and right tails of the three stock markets were larger than before the financial crisis, reaching 0.39, 0.37 and 0.30, respectively. The asymmetry between the left and right tails has increased since the financial crisis.
The empirical results of the MQCC method in the stock markets have brought some inspiration to investors. The MQCC method accurately detects the tail correlation in the stock markets more strongly than it does the correlation in other quantiles. Such results may be explained by the herd effect in behavioral finance. Investors often have a herd mentality, and their reactions to extreme returns are usually strong. More specifically, the MQCC method also reveals that the left tail correlation in the stock market is stronger than the right tail correlation. Such phenomena may be related to risk aversion in behavioral finance. Most investors in the stock markets are risk-averse. Investors are often more sensitive when facing extreme negative returns (left tail), that is, they overreact. However, when they face extreme positive returns (right tail), the response is often not as strong as when they face negative returns, which is called underreaction. In addition, the results of the MQCC method indicate that the correlation of the time series of stocks increases as the time scale increases. The implication for investors is that, when judging the price dependence of two markets based on historical price information, they should not be limited to the original daily sequence’s information. Appropriately pulling the time scale will allow investors to observe clearer long-term trends. Investors in the stock market should be more cautious when facing extreme returns, and reduce herd behavior. In this way, investors are more likely to make investment decisions rationally.
6.2. Gold Market
The development of the gold markets has increased the number of investment channels for investors, which can largely diversify investment risks and play a role in preserving and increasing value. In addition, the gold markets have provided countries with new tools for monetary policy operations. In other words, countries can adjust the composition and quantity of international reserves by buying and selling gold in the gold markets, and thus further control the money supply. This paper mainly analyzes the correlation between returns in the LONDON Gold market in the UK, the COMEX Gold market in the US, and the SHFE Gold market in China. These three gold markets are also distributed across different continents, and occupy an indispensable position in the international gold markets. Similarly, the traditional correlation coefficient method is used to test the correlation of the gold markets, as shown in the
Figure 10. LONDON Gold and COMEX Gold have always maintained a high positive correlation, and the correlation coefficient between them has been greater than 0.9. Although the correlation between LONDON Gold and SHFE Gold, and COMEX Gold and SHFE Gold, is not as strong as that between LONDON Gold and COMEX Gold, they have all maintained a relatively high level of positive correlation. Compared with stock series, the correlation between gold series tends to be stable when the time scale is at a medium level or above. More subtle measurement results should also be expressed through the MQCC method.
Figure 11 provides the results of the correlation between gold time series measured by the MQCC method. Overall, the correlation between the returns of the gold markets is stronger than that of the stock markets, and it also shows a clear positive correlation. With the increase of time scale, the correlations between COMEX Gold and SHFE Gold, and LONDON Gold and SHFE Gold, get stronger. At the level of raw data, the quantile correlation coefficients between COMEX Gold and SHFE Gold, and LONDON Gold and SHFE Gold, fluctuated within the ranges of [0.19, 0.37] and [0.19, 0.39], respectively. When the observed time scales were lower
, the corresponding quantile correlation coefficients changed, to fluctuate within the ranges of [0.58, 0.91] and [0.60, 0.95]. However, with medium and high time scales
, the returns of COMEX Gold and SHFE Gold, and LONDON Gold and SHFE Gold, showed strong correlation, and the quantile correlation coefficients were in the intervals [0.78, 1] and [0.88, 1]. In contrast, the quantile correlation coefficients of returns between LONDON Gold and COMEX Gold have not changed significantly over time. The returns of these two markets have maintained a high correlation for a long time, with correlation coefficients greater than 0.83. From different quantile levels, the results of the gold markets and the stock markets are exactly the opposite. The correlation between each pair in the three gold markets was higher in the right tail
than the left tail
. In the left tail, the quantile correlation coefficients of the returns of COMEX Gold and SHFE Gold, LONDON Gold and SHFE Gold, and LONDON Gold and COMEX Gold fluctuated in the [0.27, 0.84], [0.22, 0.99] and [0.83, 0.95]. In the right tail, the corresponding quantile correlation coefficients fluctuated in the ranges [0.31, 1], [0.31, 1] and [0.90, 1] respectively. When the quantile was around 0.95 and the time scale around 10, two of the three gold markets had the strongest correlation.
The tail correlation difference and tail symmetry of the returns between the gold markets are shown in
Figure 12 below. Compared with the 0.5 quantile correlation coefficient, the correlation difference between the right tail and the 0.5 quantile is greater than the left tail. The difference between the left tail correlation coefficients and the 0.5 quantile correlation coefficient of the returns of COMEX Gold and SHFE Gold, LONDON Gold and SHFE Gold, and LONDON Gold and COMEX Gold fluctuated within the ranges of [−0.17, 0.08], [−0.09, 0.07] and [−0.14, −0.03]. In particular, the left tail correlation coefficients of LONDON Gold and COMEX Gold were always lower than the 0.5 quantile correlation coefficient. The difference between the right tail and the 0.5 quantile correlation coefficient fluctuated within the ranges of [−0.15, 0.21], [−0.08, 0.20] and [−0.08, 0.12]. The result of the tail correlation symmetry metric
show that there was also asymmetry in the tail correlation of the returns between gold markets, and the right tail was significantly stronger than the left tail. The maximum difference between the right tail and the left tail of COMEX Gold and SHFE Gold was up to 0.31. Such difference could be as high as 0.19 in LONDON Gold and SHFE Gold, and as high as 0.24 in LONDON Gold and COMEX Gold.
Overall, there is a long-term positive correlation between the gold price series, which may be related to the precious metal characteristics of gold. Gold has a certain degree of value preservation function, and the price fluctuations in the gold market are less affected by human factors. If investors in the financial market tend to maintain their value, then gold products will be a good choice. Unlike in the stock market, the MQCC revealed that the right tail correlation in the gold price series is stronger than the left tail. This shows that the gold market is more likely to move together during the bull market. In the face of extreme positive returns on gold assets, investors’ reactions are relatively strong, and investors’ risk aversion is more pronounced. Although gold has a certain degree of value preservation function, investors should also remain rational and avoid tail risks as much as possible.
6.3. Foreign Exchange Market
The US dollar index is an indicator that reflects changes in the exchange rate of the US dollar in international foreign exchange markets, and is a standard for changes in the exchange rate of the US dollar. The public can judge the current value of the US dollar from the US dollar index, and infer possible changes in the market situations of the foreign exchange markets. Therefore, the US dollar index can be used as a tool to measure the value of the US dollar, from which people can judge the flow of capital and capital output in the US. Therefore, this paper selects the US dollar index as the main research object, and studies the correlation between the US dollar index (DINIW) and internationally important exchange rates (EURUSD, USDCNY and EURCNY). The results of measuring the correlations between foreign exchange markets through traditional correlation coefficients are shown in the
Figure 13 below. Unlike the stock market and the gold market, the overall correlation in the foreign exchange market shows a positive correlation, while some aspects show a negative correlation. Obviously, this type of measurement is still a bit rough.
The precise measurement results of the MQCC method in the foreign exchange markets are shown in
Figure 14. On the whole, DINIW has the strongest correlation with EURUSD, followed by the DINIW and EURCNY, and the weakest correlation between returns was found in the DINIW and USDCNY. Among them, the DINIW and EURUSD, and the DINIW and EURCNY, showed negative correlation, while the DINIW and USDCNY showed a positive correlation. The quantile correlation coefficients between the DINIW and EURUSD did not change significantly on different time scales, and the quantile correlation coefficients were all less than –0.90, which means that the two markets have always maintained high negative correlation. The reason for this result may be related to the composition of the DINIW. The DINIW is calculated based on the geometric average weighted value of changes in the exchange rates of the six currencies against the dollar; the Euro is one of these six currencies, and accounts for 57.6%. With the increase of the time scale, the positive correlation between the DINIW and USDCNY has gradually increased. At the original data level
, the quantile correlation coefficients between the DINIW and USDCNY were between [0.04, 0.21]. On the lower time scales
and on the higher time scales
, the quantile correlation coefficients between the two foreign exchange indices were between [0.15, 0.41] and [0.17, 0.57], respectively. With the increase of scale, the negative correlation between the DINIW and EURCNY strengthens.
The difference and symmetry analysis results for the tail correlation between the foreign exchange markets are shown in
Figure 15. Compared with the 0.5 quantile correlation coefficient, the tail correlation difference between the DINIW and EURUSD is not obvious. The left and right tails of the DINIW and USDCNY, and the right tail of the DINIW and EURCNY, are significantly different from the 0.5 quantile correlation coefficient. Among them, the difference between the left tail and the 0.5 quantile correlation coefficient of the DINIW and USDCNY was up to 0.27, and the difference between the right tail and the 0.5 quantile was up to 0.33. In addition,
shows that there was significant asymmetry in the tail correlation between the DINIW and USDCNY, and DINIW and EURCNY, in these three foreign exchange markets. The positive correlation between the right tails of the DINIW and USDCNY was significantly stronger than that for the left tails, with a difference of up to 0.24. For the DINIW and the EURCNY, the negative correlation at the left tail was stronger than the negative correlation at the right tail. This tail difference could be as high as 0.17.
In contrast, the results of the MQCC method for the foreign exchange markets are significantly different from those in the stock and gold markets. With the change of time scale, the correlations between foreign exchange price series have no consistent rules. Among them, the change in the correlation between DINIW and EURCNY was most obvious as the time scale increased. In addition, the tail correlation revealed by MQCC also has no consistent rules. For example, the right tail correlation of DINIW and USDCNY was stronger than the left tail correlation, while the left tail negative correlation of DINIW and EURCNY was stronger than the right tail negative correlation. Such results may be related to the special status of the foreign exchange markets. As a tool of payment and settlement, foreign exchange is an important international reserve of every country. The price changes between foreign exchanges are not only affected by market information, but also by the foreign exchange adjustment policies of governments. Investors in the foreign exchange market should not only pay attention to the information of the historical price of foreign exchange, but also always pay attention to the current political information regarding the governments of various countries.