Abst ract . T his paper present s t he result s of mult ifract al t est ing of two set s of financial dat a: daily dat a of t he Dow J ones Indust rial Average (DJ IA) index and minut ely dat a of t he Euro St oxx 50 index. W here mult ifract al scaling is found, t he spect rum of scaling exponent s is calculat ed via Mult ifract al Det rended F luct uat ion Analysis. In bot h cases, furt her invest igat ions reveal t hat t he t emporal correlat ions in t he dat a are a more significant source of t he mult ifract al scaling t han are t he dist ribut ions of t he ret urns. It is also shown t hat t he ext reme event s which make up t he heavy t ails of t he dist ribut ion of t he Euro St oxx 50 log ret urns dist ort t he scaling in t he dat a set . T he most ext reme event s are inimical t o t he scaling regime. T his result is in cont rast t o previous findings t hat ext reme event s cont ribut e t o mult ifract ality.
Int roduct ionMult ifract al analysis has proved t o be a valuable met hod of capt uring t he underlying scaling st ruct ure present in many types of syst ems via generalised dimensions [1] and f (α) spect ra [2]. T hese syst ems include diff usion limit ed aggregat ion [3][4][5], fluid flow t hrough random porous media [6], at omic spect ra of rare-eart h element s [7], clust erclust er aggregat ion [8] and t urbulent flow [9]. In physiology, mult ifract al st ruct ures have been found in heart rat e variability [10] and brain dynamics [11], and mult ifract al analysis has been helpful in dist inguishing between healthy and pathological patients [12]. Mult ifract al measures have also been found in man-made phenomena such as t he Int ernet [13], art [14] and the stock market [15][16][17].T he concept of mult ifract ality was first int roduced in t he cont ext of t urbulence. It was soon applied t o finance because of it s heavy t ails and long-t erm dependence. T hese two feat ures are also argued t o be present in financial dat a [18,19]. P erforming mult ifract al analysis helps t o increase our knowledge about t he financial syst em and furt her charact erise it . Many st udies have found mult ifract al scaling in financial dat a [20][21][22][23]. An underst anding of t his mult ifract al st ruct ure can enable deeper underst anding of t he dynamics of financial market s. If it is found t o be a universal feat ure of financial dat a, it provides an addit ional benchmark by which t o measure t he fitness of financial models. This in turn can help in the design of well performing port folios and in risk management [17]. a e-mail: elena.s.green@nuim.ieThe Multifractal Model of Asset Returns (MMAR) was int roduced by Mandelbrot et al. [24] as an explanat ion of t he volat ility clust ers in financial dat a and t o include "out liers", large deviat ions which make up t he fat t ails of t he ret urn dist ribut ion. T he MMAR was present ed as an alt ernat ive t o Aut oregressive Condit ional Het eroscedast icity (ARCH) models which were int roduced by Engle [25] t o account for volat ility clust er...