How Science Works
Opinions & Evidence
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Opinion
Opinion
Opinion is a personal viewpoint held by an individual. Everyone is
entitled to hold their own opinion.
It is important that you are able to distinguish between an opinion,
based on preference, hearsay, or prejudice, and a scientific opinion
which is testable and backed up with evidence.
Opinion
People have their own opinions about paintings...
Mona Lisa by
Leonardo da Vinci
The Fighting Temeraire by Constable
These are two world famous paintings. Many artists consider them
to be exceptional pieces of art , …… others may not like them.
Opinion
What one person likes another may dislike - it is only a matter of
opinion. People have different opinions on many topics...
 Music
 Architecture
 Fashion
 Literature
If one person ‘likes’ a particular painting or piece of music, their
liking is based on a personal preference and not on any factual
evidence.
Testable Opinions
A testable opinion is one that can be tested by collecting evidence.
Evidence is data (information).
Example: Suppose your best friend tells you…
Testable Opinions
“My strawberries
are the best in
the road.”
You may disagree...
This is your friend’s opinion.
It is not testable.
“I have tasted better
strawberries from
next door.”
Testable Opinions
However, it would be different if your friend told you that his
strawberries are the best because they are the biggest strawberries
grown in his road.
This statement is testable...
Testable Opinions
 You could carry out an investigation into strawberry size.
 You could visit all the strawberry growers in your friend’s road
and record the measurements of a sample of their strawberries.
This would provide evidence that would allow you to support or
refute your friend’s statement.
Testable Opinions
You may still disagree with your
friend because, in your opinion,
size is not the only indicator of
the best strawberry.
You may think that flavour
and colour play an
important part
as well.
However, you could
not refute the statement if,
having collected measurements, the data shows that your friend
does in fact grow the biggest strawberries in his road.
Testable Opinions
Read these opinions and decide if they are testable or not...
Scientific Opinions
When discussing a topic such as global warming, scientific opinions
should be testable opinions which are supported by evidence.
Evidence is data which supports the opinion, e.g. it is not scientific
to say,
“I don’t think global warming is taking place because
the weather seems normal to me.”
This opinion is not testable, and is not backed up with evidence.
Scientific Opinions
However, it is scientific to say,
“I think global warming is taking place because the polar ice
sheet has melted substantially in the last ten years.”
This opinion is testable and is backed up with evidence.
Reliable & Valid Evidence
Evidence should be reliable and
valid.
Reliable evidence is repeatable
under the same conditions.
Valid evidence is data that has
been recorded and interpreted
correctly. Valid evidence must be
reliable.
Reliable & Valid Evidence
Reliable evidence is not
necessarily valid...
...if you keep measuring, but
each time you take the
reading incorrectly, your data
will be reliable, but not valid!
Interpretation
Evidence: A strawberry on plant A has a length of 5cm.
A strawberry on plant B has a length of 3cm. This data is reliable;
the measuring was accurate .
Plant A
Plant B
If we interpret this data to conclude that Plant A produces longer
strawberries than Plant B, this is invalid, because you have not
collected sufficient data.
End of Show
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