Key Area 2 - Experimentation

Question 1

Experimentation

Question 2

Define validity

Answer 2

Validity: variables controlled so that any
measured effect is likely to be due to the
independent variable.

Question 3

Define reliability

Answer 3

Reliability: consistent values in repeats and
independent replicates.

Question 4

Define accuracy

Answer 4

Accuracy: data, or means of data sets, are
close to the true value.

Question 5

Define precision

Answer 5

Precision: measured values are close to each other.

Question 6

Pilot Study

Question 7

What is a pilot study used for?

Answer 7

Integral to the development of an
investigation, a pilot study is used to help
plan procedures, assess validity and check
techniques.

Question 8

What does a pilot study allow?

Answer 8

This allows evaluation and modification of
experimental design.

Question 9

What can a pilot study ensure?

Answer 9

The use of a pilot study can ensure an
appropriate range of values for the
independent variable.

In addition, it allows the investigator to
establish the number of repeat
measurements required to give a
representative value for each independent
datum point.

Question 10

Experimental design - Independent & Dependent Variables

Question 11

What is an independent variable?

Answer 11

An independent variable is the variable that is changed in a scientific experiment.

Independent and dependent variables can be continuous or discrete.

Question 12

What is a dependent variable?

Answer 12

A dependent variable is the variable being
measured in a scientific experiment.

Independent and dependent variables can be continuous or discrete.

Question 13

What do experiments involve?

Answer 13

Experiments involve the manipulation of the independent variable by the investigator.

Question 14

What is the experimental treatment group compared to?

Answer 14

The experimental treatment group is
compared to a control group.

Question 15

Explain the use and limitations of simple (one independent variable) and multifactorial (more than one independent variable) experimental designs

Answer 15

The control of laboratory conditions allows
simple experiments to be conducted more
easily than in the field. However, a drawback of a simple experiment is that its findings may not be applicable to a wider setting.

A multifactorial experiment involves a
combination of more than one independent variable or combination of treatments.

Question 16

What are observational studies good at detecting?

Answer 16

Observational studies are good at detecting
correlation, but since they do not directly test a hypothesis, they are less useful for
determining causation.

In observational studies the independent
variable is not directly controlled by the
investigator, for ethical or logistical reasons.

Question 17

Experimental design - Confounding variables

Question 18

Due to the complexities of biological systems, other variables besides the independent variable may affect the dependent variable.

Why must confounding variables be held constant as much as possible?

Answer 18

These confounding variables must be held
constant if possible, or at least monitored so that their effect on the results can be
accounted for in the analysis.

In cases where confounding variables cannot easily be controlled, a randomised block design could be used.

Question 19

Explain randomised blocks of treatment and control groups

Answer 19

Randomised blocks of treatment and control groups can be distributed in such a way that the influence of any confounding variable is likely to be the same across the treatment and control groups.

Question 20

Experimental design - Controls

Question 21

What are control results used for?

Answer 21

Control results are used for comparison with the results of treatment groups.

Question 22

Name the two types of controls used

Answer 22

Negative and positive controls may be used.

Question 23

Explain a positive and negative control

Answer 23

A positive control is a treatment that is included to check that the system can detect a positive result when it occurs.

The negative control provides results in the
absence of a treatment.

Question 24

What is the use of a placebo?

Answer 24

Placebos can be included as a treatment
without the presence of the independent
variable being investigated.

Question 25

Explain the placebo effect

Answer 25

Placebo effect is a measurable change in the dependent variable as a result of a patient’s expectations, rather than changes in the independent variable.

Question 26

Experimental design - In Vivo & In Vitro Studies

Question 27

Explain in vitro

Answer 27

In vitro refers to the technique of performing a given procedure in a controlled environment outside of a living organism. Examples of in vitro experiments: cells growing in culture medium, proteins in solution, purified organelles.

Question 28

Give advantages and disadvantages of in vitro

Answer 28

Advantages: less expensive, less time consuming. Disadvantages: less precise, incomplete representation of the in vitro system.

Question 29

Explain in vivo

Answer 29

In vivo refers to experimentation using a whole, living organism.

Question 30

Give advantages and disadvantages of in vivo

Answer 30

Advantages: more precise, accurate representation of in vivo. Disadvantages: expensive, more time consuming.

Question 31

Sampling

Question 32

Explain random sampling

Answer 32

In random sampling, members of the population have an equal chance of being selected.

Question 33

Explain systematic sampling

Answer 33

In systematic sampling, members of a population are selected at regular intervals.

Question 34

Explain stratified sampling

Answer 34

In stratified sampling, the population is divided into categories that are then sampled proportionally.

Question 35

Reliability

Question 36

Explain the precision and accuracy of repeated measurements

Answer 36

The reliability of measuring instruments or procedures can be determined by repeated measurements or readings of an individual datum point. The variation observed indicates the precision of the measurement instrument or procedure but not necessarily its accuracy.

Question 37

Explain how the natural variation in the biological material being used can be determined

Answer 37

The natural variation in the biological material being used can be determined by measuring a sample of individuals from the population.

Question 38

What will the mean give?

Answer 38

The mean of these repeated measurements will give an indication of the true value being measured.

Question 39

What is the range of values?

Answer 39

The range of values is a measure of the extent of variation in the results. If there is a narrow range then the variation is low.

Question 40

What should be carried out to produce independent data sets.

Answer 40

Independent replication should be carried out to produce independent data sets. Overall results can only be considered reliable if they can be achieved consistently.

Question 41

What should independent data sets be compared to to determine what?

Answer 41

These independent data sets should be compared to determine the reliability of the results.

Question 42

Presentation of Data

Question 43

What do discrete and continuous variables give rise to?

Answer 43

Discrete and continuous variables give rise to qualitative, quantitative, or ranked data

Question 44

Explain qualitative data

Answer 44

Qualitative data is subjective and descriptive.

Question 45

Explain quantitative data

Answer 45

Quantitative data can be measured objectively, usually with a numerical value.

Question 46

Explain ranked data

Answer 46

Ranked data refers to the data transformation in which numerical values are replaced by their rank when the data are sorted from lowest to highest.

Question 47

What exists if there is a relationship between two variables?

Answer 47

Correlation exists if there is a relationship between two variables.

Question 48

What is correlation?

Answer 48

Correlation is an association and does not imply causation. Causation exists if the changes in the values of the independent variable are known to cause changes to the value of the dependent variable.

Question 49

What is a positive correlation?

Answer 49

A positive correlation exists when an increase in one variable is accompanied by an increase in the other variable.

Question 50

What is a negative correlation?

Answer 50

A negative correlation exists when an increase in one variable is accompanied by a decrease in the other variable.

Question 51

Explain the strength of correlation

Answer 51

Strength of correlation is proportional to spread of values from line of best fit.