The phrase "are extremely frequent" is correct and usable in written English.
You can use it to describe something that occurs very often or with high regularity.
Example: "In urban areas, traffic jams are extremely frequent during rush hour."
Alternatives: "occur very often" or "happen with high frequency."
Covenants have rarely been the actual instruments by which societies actually functioned for long, but they are extremely frequent as ideological foundations for sociopolitical legitimacy.
As opposed to the previous two cases, face-to-face contacts are extremely frequent and appear to be the most important mode of co-ordination in close co-operation between producers and users.
In recent years, it became apparent that these serious peri-implant biological complications are extremely frequent, and the incidence of mucositis has been reported to be around 80% and that of peri-implantitis between 28 and 56% (Lindhe et al. 2008).
Caries and Periodontitis are extremely frequent human diseases with high socioeconomic impact.
Note that twitches of finger muscles are extremely frequent during normal REM sleep, and even more during REM sleep behavior disorder [25], so that a replay of learned fingers movements could not be easily distinguished from multiple and non-specific twitches during the REM sleep.
Changes of chromosome 17 copy number (aneusomy) are extremely frequent in breast cancer [ 10].
As a matter of fact, in one of the early attempts to classify willows, Wichura (1865) found hybrids to be generally rare, although they could be extremely frequent locally, leading Darwin (1865) to express his bewilderment at the "extreme frequency of hybrid willows".
Whatever problems the samurai wasp may cause in the United States, the current alternative for stemming stinkbug damage is extremely frequent applications of a broad-spectrum pesticide.
Osteoporosis is extremely frequent in post-menopausal women; nevertheless, osteoporosis in men is also a severe and frequently occurring but often underestimated disease.
An epidemiological study (EPIPPAIN) conducted in neonatal and pediatric intensive care units in France in 2005 showed that painful procedures were extremely frequent and that analgesics treatments varied a lot among units.
The program is usually structured so that right answers are apt to be extremely frequent (perhaps 95percentt of the time)—in order to encourage students, so the theory goes, and give them a feeling of success.
