involves the removal of initials in compound words, such as dropping the t in jīntiān 'today' or the ch in fēicháng 'extremely, very'. These reductions are not necessarily a function of speed of speech than of register, as it is more commonly used in casual conversations than in formal contexts. Tone quality Like all varieties of Mandarin, Guoyu is a tonal language. Putonghua as spoken in the mainland has five tones, including the neutral tone. Tones in Guoyu differ somewhat in pitch and contour. Research suggests that speakers of Guoyu articulate the second and third tones differently from the standards of Beijing Mandarin. The precise nature of the tonal differences is not well attested, however, as relevant studies often lack a sufficiently large variety of speakers. Tones may vary based on age, gender, and other sociolinguistic factors, and may not even be consistent across every utterance by an individual. In general, for Guoyu speakers, the second tone does not rise as high in its pitch, and the third tone does not "dip" back up from the low, creaky voice range. Overall, Guoyu speakers exhibit a lower and more narrow pitch range than speakers of the Mandarin of Beijing. Acoustic analysis of 33 Mandarin speakers from Taiwan in 2008 also found that for many speakers, the second tone tends to have a dipping contour more akin to that of the prescriptive third tone. Standard pronunciations compared to Putonghua In addition to differences in elision and influence from Minnanyu, which are not features that are codified in the standard Guoyu, there are differences in pronunciation that arise from conflicting official standards in Taiwan and the mainland. Quantification of the extent of pronunciation differences between Guoyu and Putonghua varies. Estimates from graduate-level research include a 2008 study, based on the 7,000 characters in the List of Commonly Used Characters in Modern Chinese, which found approximately 18% differed between Guoyu and Putonghua, and 13% for the 3,500 most commonly used characters. A 1992 study, however, found differences in 22.5% of the 3,500 most common characters. Much of the difference can be traced to preferences of linguistic authorities on the two sides; the mainland standard prefers popular pronunciations in northern areas, whereas the Taiwanese standard prefers those documented in dictionaries in the 1930s and 1940s. The Taiwanese formal standards may not always reflect actual pronunciations commonly used by actual Taiwanese speakers of Guoyu. The following