The phrase "are based principally" is correct and usable in written English.
It can be used when discussing the main foundation or primary source of something, often in academic or formal contexts.
Example: "The conclusions of the study are based principally on the data collected over the past five years."
Alternatives: "are primarily based" or "are mainly founded".
State Department personnel are based principally in the Green Zone in Baghdad and in provincial reconstruction teams at 10 locations around the country.
There is a host of arguments under this title; all of them are based principally on conceptual, a priori grounds which do not involve a posteriori empirical investigation.
These techniques are based principally on studying facial features, especially eye state [3 5], head pose [6, 7], or mouth state [8].
The weights that have been developed are based principally on two ideas: term weighting, where the importance of a term is proportional to the frequency with which a term occurs in an individual document or query; and inverse document frequency weighting, where the importance of a term is inversely proportional to its frequency of occurrence within the database as a whole [23 25].
These estimates are "based principally on old data, which was gathered mainly by the Soviets during their occupation of Afghanistan from 1979 1989" and "Stephen Peters, the head of the USGS's Afghanistan Minerals Project, said that he was unaware of USGS involvement in any new surveying for minerals in Afghanistan in the past two years.
RDTs for malaria are based principally on the detection of one of three antigens, histidine-rich protein-2 (HRP2), lactate dehydrogenase (LDH), and aldolase.
The geologic time scale is based principally on the relative ages of sequences of sedimentary strata.
She was the first woman to hold the Slade chair of fine art at Cambridge University (1967-68), and was based principally at the Courtauld Institute of Art in London.
Mr. Bloomberg, whose company's success was based principally on service, appears constitutionally opposed to cutting back, even on programs that benefit just a few.
In fact, all such economic transformations were based principally on new ideas and exciting innovation, as Joseph Schumpeter, the economic exponent of creative destruction, so clearly pointed out.
But Tibetans say the bond was based principally on a shared religion, and they argue that the Mongols did not represent the Chinese.
