to say or think that something is the result of a particular thing:
attribute something to something:
Her success can be attributed to three main factors
Hence we may say X is attributed to Y, meaning that people believe X results from Y.
Where there is some doubt about the attribution, it seems reasonable to qualify such a definite statement by saying X is likely attributed to Y, meaning that there is a probability less than 100% that Y caused X.
For example, Ill health is likely attributed to poverty implies the possibility and probability that poverty contributes to ill health, but avoids the incorrect certainty of Ill health is attributed to poverty, a statement that ignores all the other causes of poverty.
Note that in legal usage, a more restrictive use of likely sometimes applies, meaning more likely than not, and therefore implying a probability of more than 50%.
Likely means more likely than not