How Science works : reliability and validity

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How Science works Reliable evidenceandValid
evidence
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Learning Objectives You should learn

• The meaning of data and evidence,
• What is meant by reliable evidence and valid
  evidence,
• What is meant by secondary evidence.

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Definitions
data evidence reliable valid
but what do they mean??
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Definitions data
data is a measurement, or measurements. For
example When you read a thermometer
the temperature readings are data.
70oC, 68oC, 66oC, 64oC, .
Strictly speaking, data is plural. So
1 datum, 2 data, 3 data, .
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Definitions evidence
evidence is data which is judged to be
relevant. For example When you investigate
cooling
the temperature data is relevant, so it is
evidence. The length of the thermometer is not
relevant, so it is not evidence.
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Definitions evidence
evidence is data which is judged to be
relevant.

• The evidence needs be
• Reliable
• and
• Valid.

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Reliability
Reliable data is evidence you can trust. If
someone else did the same experiment, they would
get the same result.
Your evidence will be more reliable if you
repeat your readings.
For example
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Reliability For example
3 students measure the time for 1 swing of a
pendulum

• Jo measures 1 swing.
• Emma measures 1 swing, but 20 times, and
  calculates the average (mean) time.
• Jack measures 20 swings and divides the time by
  20.

Physics for You page 359
Discuss which method is the most reliable, and
why.
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Validity
Valid data is evidence that is reliable and
which is relevant to the question being
investigated.
Just being reliable evidence is not enough. The
evidence has to be relevant as well.
For example
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Validity
Discuss which of the following is valid evidence
Example 1 Measuring the length of a magnet to
decide its strength?
No, this is not valid evidence. A long magnet can
be strong or weak, and a short magnet can be
strong or weak.
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Validity
Discuss which of the following is valid evidence
Example 2
Measuring the extension of a spring to find the
force pulling on it?
Yes, this is valid evidence.
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Validity
Discuss which of the following is valid evidence
Example 3
Measuring the volume of a firework to find the
energy in it?
No, this is not valid evidence. A large or a
small firework can have a lot of energy or very
little energy,depending on the chemicals inside.
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Secondary evidence
Secondary evidence is data collected by someone
else.
You may find it in a book or on the
internet BUT You should always check to see if it
is reliable and valid.
For example
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Secondary evidence
Secondary evidence is data collected by someone
else.

Example 1 Some data on the pollution from a car
is published by the car manufacturer.
Would you trust this evidence, without further
data?
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Secondary evidence
Secondary evidence is data collected by someone
else.
Example 2
Some data on the radiation emitted from a mobile
phone is published by the phone company.
Would you trust this evidence, without further
data?
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Learning Outcomes You should now understand

• The meaning of data and evidence,
• What is meant by reliable evidence and valid
  evidence,
• What is meant by secondary evidence.

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