“If you ask a group of graphologists to study the same piece of handwriting, they all come out with different interpretations. It’s no different from astrology or numerology.” From an article on the science of Graphology
One of the most important things about research is that it should repeatable or be open to replication. So when different people come up with different results from the same data it can only be seen as opinion based not on fact.
But even careful use of hard data we may not be right. There is a certain amount of interpretation as to how to approach the data you have in front of you. So the question is how good is that interpretation, because if the data is all you need then a computer can give you the answer and that is certainly never the case.
What is agreed upon is that certain sets of techniques and interpretations are worth pursuing at any one time (and I must stress at a time). They are not always correct. Read Thomas S Kuhn’s The Structure of Scientific Revolutions and you will understand even groups of people can get things wrong. We are more manipulated by our language and culture than we would like to believe even in our age of post-Kuhn-ism.