Multifractal analysis of the intraday five-minute high-frequency data of Shanghai Stock Exchange Composite(SSEC) was conducted by utilizing the partition function method,resulting in linear mass exponent functions τ(q).Shuffled series generated by bootstrapping were used to perform a careful scrutiny on the extracted multifractal spectra f(α).It is found that the multifractal features in about 51% trading days are statistically insignificant.Moreover,the singularity strength of the real data is ...