"Stem-cell expert Roger Pedersen takes a 'glass half full' view of the findings (that embryonic stem cells cultured in the lab accumulate an alarming array of genetic changes), because the billions of archived cells seemed normal."

What does "galss half full" mean? Cautious, doubtful, 'not complete'?

Anyway, is it common to use this figurative phrase?
Emotion: smile
'Glass half-full' typically means an 'optimistic' view. 'Glass half-empty' means a 'pessimistic' view.
Students: Are you brave enough to let our tutors analyse your pronunciation?
Emotion: smile Thank you, Davkett, but from its context, professor Roger doesn't agree with the findings.
Your quoted sentence says Petersen takes [an optimistic] view 'because the...cells seemed normal.' He appears to be taking an optimistic approach to 'negative' findings, by disagreeing with the findings. He finds the cells to be normal while the 'findings' he disagrees with apparently see the cells as abnormal.
Bin-go! I never thought it in this way.

Thank you, Davkett. Emotion: smile
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