3.2. Multifractal Detrended Cross Correlation Analysis (MFDCCA)
To compute the cross-correlation between FSI and commodity indices’ daily changes, we applied the existing multifractal detrended cross-correlation analysis. We determined the variability function
Fxyq (
S)) by increasing scaling order
q from −5 to 5 step by step length, in line with the number of observations.
Figure 3. plots the log - log movement of
Fxyq (
S)) depends on the time span
s (days) between FSI and commodity indices’ daily changes of CRBI (Panel-A), BDI (Panel-B), LME (Panel-C) and BROIL(Panel-D). The lines rising from lowest to the highest relate to subsequent scale orders
for q = -5, q = 0, and q = +5. It is clear that
is well-shaped and exhibits an increasing trend with the gradual linear rise with the scale
s orders, showing there is a power law correlation between FSI and four time series of commodity indices.
The result of the Hurst exponent between FSI and commodity market returns shows a declining trend as the order of q increases. As the highest value of
Hxy(q) for FSI-BROIL reported in (column 5)
Table 3, is 0.672 when q=-5, decreases to 0.540 at q=0 and further declines to 0.472 when q=5. A similar pattern is observed in the FSI-BDI pair Hurst index i.e., 0.648, 0.581 and 0.455 at q=-5, q=0 and q=5 respectively. The same pattern is followed by the FSI-CRBI pair, the highest Hurst index 0.633 when hq=-5, while 0.543 and .507 when hq=0 and hq=5 respectively. The lowest Hurst index score is found in the FSI-LME pair, which is 0.612 with the order of q=-5, declining to 0.545 with the order of q=0 and reaching 0.496 with the order of q=5. The declining structure is found in the Hurst exponents of all FSI and commodity market index pairs. The declining trend is evidence of multifractality in the time variations in the pairs of FSI and commodity market indices’ daily change. The results show that the Hurst exponent scores between FSI and selected commodities’ return series behave with a declining trend, as long as the time scale rises. Further, they show that
values for
are all greater than the values of
, confirmation of the more persistent cross correlation pattern for minor variations than for large variations. Moreover, large variations have week cross-correlation compared to small variations, because
for smaller and large variations declines as the order of scaling
rises.
The
Table 3 further reports the findings of
, which quantify the level of persistence among the cross correlations of the FSI and commodity market indices’ returns. Interestingly, the
Hxy(q=2) score for FSI and the commodities CRBI and BROIL is greater than 0.5, which is evidence of the persistent behavior between the FSI and the selected commodity market indices’ daily price change.
Three different interpretations of these data are offered by the literature. A cross-persistent series is represented by
Hxy(2)>0.5, and a positive (negative) value of
, denotes a significant probability of another positive (negative) value of
as claimed by [
92]. [
86] and [
93] assert that long-term cross correlation implies that each series has a long memory of both its own past values and the past values of the other series. According to [
94], power-law cross-correlations show that a change in one series will be followed by a change in the other. Considering these ideas, we can claim that a rise (fall) in the FSI is likely to be followed by a decrease (increase) in commodity market prices’ daily change.
Table 4 reports the summary of the multifractal indices. The Hurst-exponent-average values lie between 0.5 and 0.6, indicating intensity or level of multifractality. However, the values of
are significantly higher than zero, establishing that the cross-correlations between FSI and commodity indices show robust multifractal patterns. A few interesting insights emerge, for instance, a degree of multifractal persistence that varies, with the maximum multifractality in the FSI-BROIL pair (∆H=0.2001) followed by FSI-BDI (∆H=0.193) then FSI-CRBI (∆H=0.126), while FSI-LME (∆H=0.125) has the lowest multifractality of the pairs under study. This shows that BROIL and BDI have the highest multifractality cross-correlation, while the LME and CRBI show a similarly low level of multifractality in the cross-correlations with FSI. These results can be confirmed by
Figure 3,
Figure 4 and
Figure 5, as well as by the results of ∆α in column 4 of
Table 4.
Figure 5 represents the association between log(s) and log (F_xyq (S)) for q=-5
(green), q=0
(red) and q=5
(black), stretched with time length s for all the pairs of FSI with commodity market indices CRBI, BDI, LME and BROIL. The log-log plots are mapped well and increasing linearly as the scale
s increases, meaning that power-law behavior and long-range cross-correlations occur between the FSI and commodity markets. The power-law cross-correlation infers that large variations in commodity market prices move to be complemented by the considerable variations in FSI and vice-versa. The higher width here is evidence of more variations, indicating random and heterogeneous distribution, which points to the more unpredictable descriptions of the daily change in commodity market indices.
The significant difference from zero spans of the cross-correlations’ multifractal progressions corroborates the obvious deviations from the random walk process. The AMH’s assumptions are backed up by evidence in favor of multifractality in the cross-correlation form [
95], which has also been demonstrated in earlier research [
96,
97,
98].
vs. α.
The degree of asymmetry results is reflected in column 5 of
Table 4. The FSI-CRBI pair represented the highest
AI value (3.968) followed by the FSI-BROIL pair (2.204) and FSI-BDI showed the lowest asymmetry AI value (1.285). Interestingly all commodity market indices paired with FSI show right skewed cross-correlations. When the value of the
cross-correlation between the pair is right skewed contrary to the
, is left skewed cross correlations. Additionally, outcomes of the singularity ratio C, a truncation gauge, for almost all the pairs indicate more profound left side tails
of the spectrum
, suggesting more potent singularities, and the cross-correlation has a multifractal synthesis that is impervious to small-scale local variations [
99].
The findings of singularity ratio
C are reported on the right side of the last column of
Table 4, where FSI-BDI is (0.7607) followed by FSI-LME (0.541) then FSI-BROIL (0.469) and the least value of FSI-CRBI (0.302). Interestingly, similar to the findings of
, all commodity market indices showed
, indicating strong singularities and the cross-correlations have a multifractal formation that reacts promptly to local fluctuations even with small variations [
99].
Past literature shows that long-range cross-correlations, fat-tails and intermittency are the main features of multifractality in the commodity markets. Cross-correlation indicates that the indices’ oscillations over longer time scales rely heavily on their past behavior rather than being independent of one another. The persistence or anti-persistence trends, loops, or volatility in the indices can lead to long-range correlations. The Hurst exponent, which runs between 0 and 1, can be used to calculate long-range correlations. An approximate Hurst exponent of 0.5 signals an arbitrary process, while an approximate Hurst exponent of 0 or 1 indicates either high persistence or anti-persistence, respectively. Fat-tails indicate the probable occurrence of extreme events (such as sharp price movements or crashes) is higher than would be estimated from a normal distribution in cases of fat-tailed distributions. The assortment of market participants, complicated feedback actions, the existence of outliers or aberrations in the data, or all these factors, can lead to fat-tailed distributions. Kurtosis, a measurement of how peaked or flat a distribution is in comparison to a normal distribution, can be used to identify fat-tailed distributions. A normal distribution is indicated by a kurtosis that is near to 3, whereas a fat-tailed distribution is indicated by a kurtosis that is higher than 3. Intermittency describes how the indices’ variations fluctuate in intensity throughout a range of time scales rather than being uniform. The multiscale structure of market activity, including the various trading frequencies, methods, and horizons of market participants, can lead to intermittent activity. The scaling exponents, which express how the fluctuations alter with the observation time scale, can be used to quantify intermittentness. A multifractal process is indicated by a changing scaling exponent, whereas a self-similar process is shown by a constant scaling exponent.
In their study of the realized volatility series of the Shanghai Stock Exchange Composite Index (SSEC) and the Shenzhen Stock Exchange Composite Index (SZSEC), [
100] discovered that both indices displayed multifractality. Additionally, they discovered that fat-tailed distributions had some effects on multifractality and that long-range correlations of minor and significant major variations were the primary drivers of multifractality. In order to look into the nonlinear dependency and multifractality in the price-volume associations of China’s and the US’s agricultural commodities’ futures markets, [
101] used multifractal detrended cross-correlation analysis (MFDCCA). They reported that both markets’ price-volume interactions demonstrated multifractality, with the main contributors being long-range cross-correlations and fat-tailed distributions.
[
102] explored the multifractal features of financial markets, including commodity markets, employing multifractal analysis techniques and multifractal models. They scrutinized the accumulating proof of multifractality in financial time series across many markets and time periods, and argued about its origins. Additionally, they highlighted how multifractal analysis might be used to assess market inefficiencies and improve risk management, along with other applications.