3.2b Experimental design

Question 1

What is an independent variable?

Answer 1

the variable that is changed in a scientific experiment

Question 2

What is a dependent variable?

Answer 2

the variable being measured in a scientific experiment

Question 3

What are the two different categories of independent and dependent variables?

Answer 3

continuous or discrete

Question 4

What do experiments involve happening to the independent variable?

Answer 4

manipulation of the independent variable by the investigator

Question 5

What is the experimental treatment group compared to?

Answer 5

a control group

Question 6

What is a simple experimental design?

Answer 6

one independent variable

Question 7

what is a multifactorial experimental design?

Answer 7

more then one independent variable

• involves a combination of more than one independent variable or combination of treatments

Question 8

What is the advantage and disadvantage of simple experimental design?

Answer 8

advantage - control of laboratory conditions allows them to be conducted more easily that in the field
disadvantage - its findings may not be applicable to a wider setting

Question 9

Explain independent variables in observational studies

Answer 9

• investigators may use groups that already exist, so there is no truly independent variable
• the independent variable is not directly controlled by the investigator, for ethical or logistical reasons

Question 10

Explain observational studies and correlation and causation

Answer 10

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

Question 11

Explain why the confounding variables effect the dependent variable

Answer 11

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

Question 12

How must confounding variables be treated in scientific experiments?

Answer 12

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

Question 13

What can you use in situations when confounding variables cannot be easily controlled?

Answer 13

a randomised block design

Question 14

Explain how to carry out a randomised block design

Answer 14

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 15

What are control results used for?

Answer 15

for comparison with the results of treatment groups

Question 16

What are the two different types of control groups?

Answer 16

• positive
• negative

Question 17

What is the role of a negative control?

Answer 17

it provides results in the absence of a treatment

Question 18

What is the role of a positive control?

Answer 18

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

Question 19

What is the placebo effect?

Answer 19

a measurable change in the dependent variable as a result of the patients expectations, rather then the changes in the independent variable

Question 20

What is a placebo?

Answer 20

included as a treatment without the presence of the independent variable being investigated

Question 21

What does “in vitro” refer to?

Answer 21

the technique of performing a given procedure in a controlled environment outside of a living organism

Question 22

What does “In vivo” refer to?

Answer 22

experimentation using a whole, living organism

Question 23

Give 3 examples of in vitro studies

Answer 23

• cells growing in culture medium
• proteins in solution
• purified organelles

Question 24

Give 2 advantages to in vitro studies and 1 disadvantage

Answer 24

Advantages
- being able to control the environment of the study
- less use of animals

Disadvantages
- it is not under the same conditions as in a cell or in an organism

Question 25

Give 2 advantages to in vivo studies and _ disadvantages

Answer 25

Advantages
- You can see side effects of treatments
- they give you a big picture view if the treatment in the whole organism

Disadvantages
- ethical dilemmas as it it involving living organisms
- Harder to control confounding variables so the results may be less reliable