The phrase "are expensive to study" is correct and usable in written English.
It can be used when discussing the costs associated with researching or analyzing a particular subject or phenomenon.
Example: "The rare species of fish are expensive to study due to their limited habitat and the specialized equipment required for research."
Alternatives: "costly to research" or "high-priced to investigate".
They are expensive to use in studies large enough to detect risks of the magnitude (probably < 2-fold) we would expect for EDCs based on the relative risks for known hormonal risk factors.
Larger RCT studies are expensive to conduct and most of the reviewed studies were unfunded.
Such studies are expensive to carry out and consequently, academic endeavours have also been directed towards the study of Benefits Transfer, where we try to infer the benefit derived from one ESA (for example) as representative of the benefit derived from another ESA.
Such studies are expensive to conduct, and few have incorporated dose responses, which are a necessary component in DRI development.
In case of TFBS, it would be extremely expensive to study half or three quarters of thousands of all possible TFBS and then make predictions in the remaining candidates.
Some issues are just too expensive to study rigorously, some are too difficult to measure reliably, and some require so many exclusions before sampling that the scope of generalisability is uncertain or limited.
This outcome demonstrates that important environmental variables can be used as effective surrogates for conservation planning where knowledge of the biology is imperfect; this can be especially helpful in marine benthic systems, which are difficult and expensive to study and often have poorer historical coverage than their terrestrial or pelagic equivalents [145].
The development of accurate chemical kinetic models capable of predicting the combustion of methane and dimethyl ether in common combustion environments such as compression ignition engines and gas turbines is important as it provides valuable data and understanding of these fuels under conditions that are difficult and expensive to study in the real combustors.
Pigs will also turn any pasture into a mud bath by rooting for food and so can be expensive to maintain in a long term study (Wolfensohn & Lloyd 2003).
