The Scientific Method

Question 1

What is validity?

Answer 1

The extent to which a measurement, test, or study measures what it appears to measure.

Question 2

What is a valid conclusion?

Answer 2

A conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning.

Question 3

What is reliability?

Answer 3

The degree of stability exhibited when a measurement is repeated under identical conditions.

Question 4

What are the three types of reliability?

Answer 4

• Repeatability
• Reproducibility
• Representativity

Question 5

What is repeatability?

Answer 5

A measurement is repeatable if the original experimenter repeats the investigation using same method and equipment and obtains the same results.

Question 6

What is reproducibility?

Answer 6

A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained.

Question 7

What is representativity?

Answer 7

A measurement is representative if the results can be generalised to a wider population.

Question 8

What is a fair test?

Answer 8

A fair test is one in which only the independent variable has been allowed to affect the dependent variable.

Question 9

What is bias?

Answer 9

Inclination or prejudice for or against one person/group/idea/belief, especially in a way considered to be unfair.

Question 10

What is accuracy?

Answer 10

A measurement result is considered accurate if it is judged to be close to the true value

Question 11

What is precision?

Answer 11

Precise measurements are ones in which there is very little spread about the mean value when you measure the same variable repeatedly with the same instrument. Precision depends only on the extent of random errors – it gives no indication of how close results are to the true value.

Question 12

What is a true value?

Answer 12

This is the value that would be obtained in an ideal measurement.

Question 13

What is uncertainty?

Answer 13

The interval within which the true value can be expected to lie, with a given level of confidence or probability.

Question 14

What is resolution?

Answer 14

This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading.

Question 15

What is the range?

Answer 15

The maximum and minimum values of the independent or dependent variables; important in ensuring that any pattern is detected.

Question 16

What is an interval?

Answer 16

The quantity between readings.

Question 17

What is calibration?

Answer 17

Marking a scale on a measuring instrument. This involves establishing the relationship between indications of a measuring instrument and standard or reference quantity values, which must be applied.

Question 18

What is data?

Answer 18

Information, either qualitative or quantitative, that has been collected.

Question 19

What is evidence?

Answer 19

Data which has been shown to be valid.

Question 20

What is a hypothesis?

Answer 20

A proposal intended to explain certain facts or observations.

Question 21

What is a prediction?

Answer 21

A prediction is a statement suggesting what will happen in the future, based on observation, experience or a hypothesis.

Question 22

What are anomalies?

Answer 22

These are values in a set of results which are judged not to be part of the variation caused by random uncertainty.

Question 23

What is a measurement error?

Answer 23

The difference between a measured value and the true value.

Question 24

What is a random error?

Answer 24

These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next.

Random errors are present when any measurement is made, and cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean.

Question 25

What is a systematic error?

Answer 25

These cause readings to differ from the true value by a consistent amount each time a measurement is made.

Sources of systematic error can include the environment, methods of observation or instruments used.

Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared.

Question 26

What is a zero error?

Answer 26

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero. A zero error may result in a systematic uncertainty.

Question 27

What is the difference between association and causation?

Answer 27

Association is just the statistical relationship between two variables, whereas causation is when one variable is a result of the other variable.

Question 28

What should you include when writing a conclusion?

Answer 28

1. Describe the data
2. Quote the figures or process the data
3. Criticise the study

Question 29

What should you discuss when criticising a study?

Answer 29

• validity: control variables, correct data
• time scales
• sample sizes, generalisability
• repeatability
• control experiments/groups
• statistical tests
• causation/association
• confounding variables/other factors

Question 30

When dissolved in water, what does an acid do to a solution?

Answer 30

An acid gives a solution more protons.

Question 31

When dissolved in water, what does a base do to a solution?

Answer 31

A base takes protons out of a solution.

Question 32

What is a pH scale the measure of?

Answer 32

A pH scale is a measure of the concentration of hydrogen ions present in solution.

Question 33

What sort of graph does a pH scale form?

Answer 33

An inverse graph. As the hydrogen ions increase, the pH number decreases.

Question 34

What kind of scale is the pH scale?

Answer 34

It is a logarithmic scale, e.g. pH5 has 10x the concentration of hydrogen ions of that of pH6.

Question 35

What is log10?

Answer 35

The power to which 10 is raised to give the requited number or the number of times you need to multiply 10 by to give the required number.

Question 36

How do you prove a causal relationship between two variables?

Answer 36

1. Establish a hypothesis to try to explain the correlation; this should be based on current knowledge.
2. Design and perform experiments to test the hypothesis.
3. Establish the causal link and formulate theories to explain it.