It is not known whether the bird died because it ingested so much debris, and it is often difficult to establish whether plastics kill marine life.
Where HIV transmission might be connected to chemsex, it is difficult to establish whether the drugs had any influence or whether those men would have engaged in unprotected sex anyway.
"It is difficult to establish whether this is because the duration itself worsens labor market prospects, or because those workers facing the strongest challenges in the labor market take longer to find a new job," Till von Wachter, a professor of economics at Columbia University, told Congress in 2010.
It is difficult to establish whether surgical intervention is necessary in IgG4-related cholecystitis.
This limitation makes it difficult to establish whether rural populations living in central Peru are protected from autoimmunity and allergy through the hygiene hypothesis mechanism.
But experts say that, with Ebola cases falling, it may be difficult to establish whether the jab offers any protection against the virus.
It is difficult to establish whether the detected fluorescence intensity originates from the fluorescent agent bound to the specific cancer receptor or it comes simply from accumulated free fluorophores inside the tumor (due to EPR effect and leaky vascularization).
It is very difficult to establish whether septic cardiomyopathy independently affects the prognosis of patients with septic shock, because many other variables are involved, such as age, patient history, type of microorganisms, and time to resuscitation.
This makes it difficult to establish whether conifers were arming themselves against taller dinosaurs or against early mammals and birds that were also beginning to appear in the late Jurassic and early Cretaceous periods.
However, there are many factors that influence the results of the experimental tests, and it is difficult to establish whether the value obtained is really representative of the material in situ and if there are alterations which have arisen in time.
By just studying Tables 8 and 9, it is difficult to establish whether there is a connection between number of organisations and the development time since number of organisations varies considerably in Table 8 (from 1 to 9) and 9 (from 0 to 5).
