1. Repeatable data, Reproducible data and Valid evidence
Working Scientifically:
Repeatable data, Reproducible data and Valid evidence

2. Learning Objectives
You should learn :
The meaning of ‘data’ and ‘evidence’,
What is meant by ‘repeatable’ data, ‘reproducible’ data, and ‘valid’ evidence,
What is meant by ‘secondary’ evidence.

3. …data …evidence …relevant …valid…
Definitions
…data …evidence …relevant …valid…
…but what do they mean??

4. 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, ….

5. 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.
The data needs be:
Repeatable, Reproducible and
Valid.

6. Repeatable
Repeatable data are measurements that when repeated by the same person, with the same equipment, give the same or similar results.
This is not a severe test of the data, because the investigator could be making the same mistakes again and again.

7. Reproducible Reproducible
Reproducible data are similar results obtained by different people with different equipment.
This is a stronger test than just being repeatable.

8. Accurate data
Your evidence will be usually be more accurate, with less uncertainty, if you repeat your readings.
Repeating your readings, and taking the mean (average) reduces the effect of random errors.
(See the PowerPoint on ‘Errors’)
For example…

9. Accurate data 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, 3 times, calculates the average (mean) time and then divides that by 20.
Discuss which method is best, and why.

10. Validity
Valid data is evidence from a fair test which is repeatable, reproducible and relevant to the question be investigated.
Just having the evidence is not enough.
The evidence has to be relevant as well.
For example…

11. Validity Discuss which of the following is valid evidence: Example 1
Measuring the length of a magnet to decide its strength? N S
No, this is not valid evidence.
A long magnet can be strong or weak, and a short magnet can be strong or weak.

12. 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.

13. 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.

14. 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 relevant and valid.
For example…

15. 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?

16. 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?