Sentence:  Furthermore , it may <WSD>be</WSD> possible to estimate the error due to bias in method ( as distinguished from sampling error ) in each of these sources , on such subjects as fertility , mortality , and migration during a given interval by using information from two largely independent sources in conjunction . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)