What is the average reproductive number for studies?
SELECT (AVG(?reproductive_number) AS ?average_reproductive_number)
WHERE {
  orkgr:R44930 orkgp:compareContribution ?contrib.
  ?contrib orkgp:P23140 ?basic_reproductive_number.
  ?basic_reproductive_number orkgp:HAS_VALUE ?value
  BIND(xsd:float(?value) AS ?reproductive_number)
}