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Statistics: > Experimental Design > Flashcards

Experimental Design Flashcards

1
Q

How are study types grouped as?

A
  • Observational

- Experimental

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2
Q

What is observational study?

A

Observations that are easily assessed/examined without interventions

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3
Q

What is an experimental study?

A

Where the hypothesis is tested using an intervention

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4
Q

How are experimental studies carried out?

A

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

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5
Q

What is the meaning of intervention?

A

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

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6
Q

What is an advantage of experimental studies?

A

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

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7
Q

What is peer-review?

A

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

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8
Q

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

A
  • Fake experts give out the information

- Results can be exaggerated

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9
Q

What is a disadvantage of observational studies?

A

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

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10
Q

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?

A
  • 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
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11
Q

What is the placebo effect?

A

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

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12
Q

What is publication bias?

A

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

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13
Q

What is a variable?

A

Anything relevant to an experiment which can be measured

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14
Q

What comes under a variable?

A
  • Evaluating what we need to measure (dependent variable)

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

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15
Q

What is the independent variable sometimes called?

A

The explanatory variable

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16
Q

What is the independent variable?

A

The variable that causes a particular outcome

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17
Q

What is the dependent variable also known as?

A

The response variable

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18
Q

What is the dependent variable?

A

The variable influenced by the independent variable

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19
Q

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

A
  • 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
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20
Q

What is a confounding variable?

A

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

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21
Q

What is the disadvantage of confounding variables in an experiment?

A
  • It makes any results obtained more difficult to decipher

- It is difficult to pick out all he confounding variables

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22
Q

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

A
  • 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
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23
Q

Why is there always a chance of error in statistics?

A

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

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24
Q

What is error?

A

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

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25
Q

Why is it good to decrease the degree of error?

A

So that the results produced are reliable

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26
Q

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

A
  • Sampling error

- Bias

27
Q

Where does error come about?

A

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

28
Q

What is sampling error?

A

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

29
Q

Why are we able to estimate the sampling error?

A
  • The sampling error is normally distributed

- Statistical tests account for take the normal distribution of sampling error

30
Q

What ways are used to reduce sampling error?

A
  • Replication
  • Balance
  • Blocking
31
Q

How does replication control sampling error?

A

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

32
Q

What are the different types of replicates?

A
  • Technical replicate

- Biological replicate

33
Q

What are technical replicates?

A

Repeating the same conditions of an experiment without changing anything

34
Q

What are biological replicates?

A

The number of different individual cells/organisms being tested on

35
Q

Name a difference between technical and biological replicates:

A

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

36
Q

How does balance reduce sampling error?

A
  • By comparing similar sized groups

- Groups of different sizes are more likely to not have equal variance

37
Q

Which statistical tests assume there s equal variance between groups?

A
  • t-test

- ANOVA

38
Q

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

A
  • The t-test and ANOVA test would not be able to be performed
  • Reduces statistical power
39
Q

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

A
  • t.test() function

- This function uses the Welch’s t-test which alters the degrees of freedom when variance between groups is not equal

40
Q

What is needed to work out statistical power?

A
  • Sample size
  • Effect size (Cohen’s d)
  • Significance level
41
Q

How does different sized samples decrease statistical power?

A
  • 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
42
Q

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

A
  • Increase
  • β= probability of getting false negative
  • Power = 1-β
  • If power decreases, β increases
  • This decreases the chances of finding true positives
43
Q

How is blocking?

A

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

44
Q

What is the advantage of blocking?

A

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

45
Q

What is bias?

A

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

46
Q

At what stage of research can bias occur?

A
  • Study design
  • Data collection
  • Data analysis
  • Publication
47
Q

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

A

By not randomly picking individuals/objects/

48
Q

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

A

Using faulty equipment

49
Q

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

A

?????????

50
Q

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

A

Results are only released if they align with hypothesis

51
Q

What methods are used to control bias?

A
  • Simultaneous control groups
  • Blinding
  • Randomisation
52
Q

What is a control group?

A

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

53
Q

What are the types of control in an experiment?

A
  • Untreated control
  • Vehicle control
  • Best available therapy control
  • Positive control
  • Negative control
54
Q

What is a vehicle control? Why is it done?

A
  • 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
55
Q

What is best-available therapy?

A

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

56
Q

What is a positive control?

A

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

57
Q

What is a negative control?

A

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

58
Q

Why are controls described as simultaneous?

A

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

59
Q

What is blinding and when is it used?

A

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

60
Q

What is randomisation?

A

Where individuals in an experiment are randomly assigned to groups

61
Q

Why might individuals not be completely randomly put into groups?

A

Control for block????

62
Q

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

A

Introduces bias so may not be truly random

63
Q

What is the placebo effect?

A

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

Statistics: (5 decks)

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