Experimental Design

Question 1

How are study types grouped as?

Answer 1

• Observational

- Experimental

Question 2

What is observational study?

Answer 2

Observations that are easily assessed/examined without interventions

Question 3

What is an experimental study?

Answer 3

Where the hypothesis is tested using an intervention

Question 4

How are experimental studies carried out?

Answer 4

By changing the variables of an experiment to determine whether a change in one affects the other

Question 5

What is the meaning of intervention?

Answer 5

Attempts made to alter the outcome of the experiment- controlling the independent variable

Question 6

What is an advantage of experimental studies?

Answer 6

All variables other than the desired independent variable are controlled, so you can see what effects the independent variable is having

Question 7

What is peer-review?

Answer 7

When a scientist present their data and the proof and other scientists critically analyse it

Question 8

What is the problem with information being given on the news/TV?

Answer 8

• Fake experts give out the information

- Results can be exaggerated

Question 9

What is a disadvantage of observational studies?

Answer 9

It indicates that there is a causal effect even if there isn’t

Question 10

What bad study design methods are used by pharmaceutical companies to show that their new drug works better than any others? Why is this done?

Answer 10

• Compare effects of drug against a placebo, which may indicate that drug works but doesn’t indicate if better than any other available drug
• Compare drug to best available drug but use best available drug at such a high dose that it has more side effects- making the new drug look better

Question 11

What is the placebo effect?

Answer 11

An outcome which has been caused by having certain beliefs or assumptions

Question 12

What is publication bias?

Answer 12

When only parts of data collected in research is shown and available to make an informed analysis of the research conducted

Question 13

What is a variable?

Answer 13

Anything relevant to an experiment which can be measured

Question 14

What comes under a variable?

Answer 14

• Evaluating what we need to measure (dependent variable)

- The independent variable that we believe is going to change the result we see

Question 15

What is the independent variable sometimes called?

Answer 15

The explanatory variable

Question 16

What is the independent variable?

Answer 16

The variable that causes a particular outcome

Question 17

What is the dependent variable also known as?

Answer 17

The response variable

Question 18

What is the dependent variable?

Answer 18

The variable influenced by the independent variable

Question 19

When, in an experiment would you not want to/can’t control every variable but the independent and depend variables?

Answer 19

• May be doing an observational study
• Conducting an experimental study which needs to mimic real scenarios, where the dependent variable is affected by many different factors

Question 20

What is a confounding variable?

Answer 20

A variable, aside from the independent variable, which also influences the dependent variable

Question 21

What is the disadvantage of confounding variables in an experiment?

Answer 21

• It makes any results obtained more difficult to decipher

- It is difficult to pick out all he confounding variables

Question 22

What can be done when all the confounding variables are identified?

Answer 22

• Limit/cancel affects of the confounding variables so it is more clear to see the effect of the independent variable
• Help identify the drawbacks of the study due to the confounding variables
• Further experiments can be made to accommodate for these drawbacks and strengthen the validity of the evidence provided

Question 23

Why is there always a chance of error in statistics?

Answer 23

Statistical tests cannot completely deem a hypothesis to be true or false, it only states the chances of it happening by chance

Question 24

What is error?

Answer 24

The difference between the data for a population and it’s sample/experiment

Question 25

Why is it good to decrease the degree of error?

Answer 25

So that the results produced are reliable

Question 26

What are the main types of error that we can control?

Answer 26

- Sampling error | - Bias

Question 27

Where does error come about?

Answer 27

When we can't measure the entire population so we take the results of a sample to represent the population

Question 28

What is sampling error?

Answer 28

Error caused by the chances that the sample doesn't represent the population entirely

Question 29

Why are we able to estimate the sampling error?

Answer 29

- The sampling error is normally distributed | - Statistical tests account for take the normal distribution of sampling error

Question 30

What ways are used to reduce sampling error?

Answer 30

- Replication - Balance - Blocking

Question 31

How does replication control sampling error?

Answer 31

More replication means that there is a large data range, which increases the how accurate and valid the results may be

Question 32

What are the different types of replicates?

Answer 32

- Technical replicate | - Biological replicate

Question 33

What are technical replicates?

Answer 33

Repeating the same conditions of an experiment without changing anything

Question 34

What are biological replicates?

Answer 34

The number of different individual cells/organisms being tested on

Question 35

Name a difference between technical and biological replicates:

Answer 35

Technical replicas can happen at the same time, biological ones cannot

Question 36

How does balance reduce sampling error?

Answer 36

- By comparing similar sized groups | - Groups of different sizes are more likely to not have equal variance

Question 37

Which statistical tests assume there s equal variance between groups?

Answer 37

- t-test | - ANOVA

Question 38

What is the effect of having an experiment with different sized samples?

Answer 38

- The t-test and ANOVA test would not be able to be performed - Reduces statistical power

Question 39

What function can be used for experiments with uneven sample sizes? Why does this work?

Answer 39

- t.test() function | - This function uses the Welch's t-test which alters the degrees of freedom when variance between groups is not equal

Question 40

What is needed to work out statistical power?

Answer 40

- Sample size - Effect size (Cohen's d) - Significance level

Question 41

How does different sized samples decrease statistical power?

Answer 41

- Standard deviation and variance are tightly linked - Standard deviation is used to work out effect size - This causes a larger combined standard deviation - This decreases statistical power

Question 42

What affect does decreased statistical power have on the probability of false negatives and true positives?

Answer 42

- Increase - β= probability of getting false negative - Power = 1-β - If power decreases, β increases - This decreases the chances of finding true positives

Question 43

How is blocking?

Answer 43

Collecting experimental units that have similar properties, where treatments are randomly allocated to each experimental unit in each block

Question 44

What is the advantage of blocking?

Answer 44

It removes the chances of an anomalous result happening due to an outside factor

Question 45

What is bias?

Answer 45

Error caused by systematic differences in our estimation of the sample data to that of the population

Question 46

At what stage of research can bias occur?

Answer 46

- Study design - Data collection - Data analysis - Publication

Question 47

How can bias occur in the study design part of an experiment?

Answer 47

By not randomly picking individuals/objects/

Question 48

How can bias occur in the data collection part of an experiment?

Answer 48

Using faulty equipment

Question 49

How can bias occur in the data analysis part of an experiment?

Answer 49

?????????

Question 50

How can bias occur in the publication part of an experiment?

Answer 50

Results are only released if they align with hypothesis

Question 51

What methods are used to control bias?

Answer 51

- Simultaneous control groups - Blinding - Randomisation

Question 52

What is a control group?

Answer 52

A group of individuals that are not treated with the independent variable and are compared to groups that are

Question 53

What are the types of control in an experiment?

Answer 53

- Untreated control - Vehicle control - Best available therapy control - Positive control - Negative control

Question 54

What is a vehicle control? Why is it done?

Answer 54

- A control which is treated the same as the experimental groups but without the main independent variable - This is to see if something else in the treatment/experiment is causing the effects observed

Question 55

What is best-available therapy?

Answer 55

When an already existing substance /drug is compared to a sample of a new one to see which works better

Question 56

What is a positive control?

Answer 56

A control that is know to produce the desired effects/expected outcomes

Question 57

What is a negative control?

Answer 57

A control known not to give the desired outcome/expected effect

Question 58

Why are controls described as simultaneous?

Answer 58

They must be carried out at the same time as experimental groups

Question 59

What is blinding and when is it used?

Answer 59

This is typically seen in clinical trials where patients and/or the doctor don't know which patients are or aren't part of the control or test group

Question 60

What is randomisation?

Answer 60

Where individuals in an experiment are randomly assigned to groups

Question 61

Why might individuals not be completely randomly put into groups?

Answer 61

Control for block????

Question 62

Why is randomisation better carried out with a machine than a person?

Answer 62

Introduces bias so may not be truly random

Question 63

What is the placebo effect?

Answer 63

Where a subject can experience the effects of a treatment/independent variable without it being administered to them