Experimental Designs, Control and Sampling

Question 1

What are the 3 types of experimental designs you need to be aware of:

Answer 1

1. Independant groups
2. Repeated measures
3. Matched Pairs design

Question 2

Describe independent groups:

Answer 2

Participants divided into [2] groups (number of groups is dependant on number of conditions)
Each group participates in one condition of the experiment, e.g. Group 1-> Condition 1

Question 3

Strengths of independent groups:

Answer 3

Since ppts partake in 1 condition, there are no order effects. As a result, ppts performance in the first condition will not be affected by boredom or fatigue. - results will not be affected by such order affects and results will only be due to IV manipulation.
- since ppts partake in 1 condition: won’t realise aim of exp- no demand characteristics shows, ppts will display natural behaviour which will lead to valid data- increase in validity of findings and conclusions drawn.

Question 4

Weaknesses of independent groups:

Answer 4

• ppt variables affect results bc 2 diff groups of ppl are being compared, and one group may be better at the task than the other. We cannot be confident that results obtained are due to the manipulation of the IV as existing differences between the ppts may end up affecting results too. Decreasing validity
• takes time as you require double the ppts

Question 5

Describe Repeated measures:

Answer 5

Ppts all in 1 group
The same group takes part in ALL conditions of the exp

Question 6

Strengths of repeated measures:

Answer 6

Ppt variables cannot affect results as ppts take part in all conditions so no individual differences between conditions that may impact results. Can be sure that differences between conditions is due to IV manipulations instead of differences between ppts- increases validity

Question 7

Weaknesses of repeated measures:

Answer 7

• since ppts partake in both conditions- may be order effects which can impact ppts performance and affect results as they will no longer be due to IV manipulation- decreases the validity.
• since ppts take part in ALL conditions- may realise aim of exp- leading to demand characteristics as ppts may change beh to suit or refute the aim of the exp.

Question 8

How are Matched pairs design used?

Answer 8

1) ppts tested on a trait, e.g IQ
2) ppts with similar scores from this test are ‘paired up’
3) one ppts from each pair is allocated to condition 1, whilst the other is allocated to condition2
4) each ppts only completes 1 condition of exp. Researcher continues to do so until desired number of ppts in each condition is met

Question 9

Strengths of matched pairs design:

Answer 9

• similarity in ppt variables makes sure there are limited individual differences between ppts- sure that difference between conditions are due to IV manipulation rather than existing differences between ppts - increase validity
• no order effects
• ppts cannot work out the aim

Question 10

Weakness of matched pairs design

Answer 10

Testing and matching ppts is time consuming and expensive

Question 11

4 different methods of control:

Answer 11

• counter balancing
• random allocation
• standardisation
• randomisation

Question 12

How we do Counter Balancing:

Answer 12

1) all ppts are divided into 2 subgroups
2) subgroup 1 will do condition A first and then condition B
3) subgroup 2 will participate in condition B first and then condition A
4) this balances out order effects between both conditions

Question 13

Why do we use counter balancing?

Answer 13

• used in repeated measures in order to balance order effects between conditions
• can be more certain that changes in DV due to IV rather than order effects

Question 14

How do we do Random Allocation?

Answer 14

1) if you have 20 ppts put 10 pieces of paper with letter A and 10 with letter B into hat
- should be equal number of paper letters A:B
2) all ppts should pick out a piece of paper from hat
3) ppts who get letter A are put in condition 1. Ppts who get B put in Condition 2
OR
For every pair, researcher can flip a coin

Question 15

Why we use Random Allocation:

Answer 15

• using chance to allocate ppts to diff conditions
• used in independent group design to avoid similar ppts all being allocated to same condition (e.g all students with GCSE 9 in maths in one condition)

Question 16

How do we do standardisation:

Answer 16

Use standardised instructions by keeping information given to ppts exactly the same throughout all conditions
Use standardised procedure- keeping the same method throughout all conditions of exp

Question 17

Why do we do standardisation?

Answer 17

Keeping everything the same within the method of the exp to ensure that one condition does not have an unfair advantage
Remove Extraneous variables and investigator effects

Question 18

How do we do randomisation:

Answer 18

1) if ppts are shown 20 images, all 20 should be put in a hat
2) researchers take the images out of the hat 1 by 1
3) the order in which the images come out of the hat is the order they will be presented to ppts

Question 19

Why do we use randomisation:

Answer 19

Using chance to establish the order in which stimuli are presented to the ppt within the exp

Question 20

Investigator effects

Answer 20

When the investigator knowingly or unknowingly demonstrates behaviour that influences the behaviour of the ppts, thus impacting findings.

Question 21

Examples of investigator effects

Answer 21

Investigators appearance
Tone of voice
Accent
Investigating script

Question 22

Examples of order effects

Answer 22

Boredom
Fatigue

Question 23

What is sampling?

Answer 23

Method of collecting ppts for your research.

Question 24

What is a target population?

Answer 24

A group of people the researcher wishes to apply the findings of the experimenter to. Usually have a trait that is of interest to the researcher.

Question 25

What is a sample:

Answer 25

A group of people from the target population who will participate in the research

Question 26

What is a representative sample:

Answer 26

When a sample is an accurate reflection of the target population it can be considered representative. As a result, the findings are generalisable to the target population

Question 27

What are the 5 types of sampling:

Answer 27

• opportunity sampling
• volunteer sampling
• random sampling
• systematic sampling
• stratified sampling

Question 28

What is opportunity sampling:

Answer 28

• researcher chooses ppts who are members of target population and are willing and able to take part
• done by approaching and asking members of the target population if they would like to partake
• researcher continues until they have the desired number of ppts

Question 29

Strength of opportunity sampling:

Answer 29

+ easiest and most convenient method as we use the first ppts you find - less time consuming and effort to aquire a sample

Question 30

Weaknesses of opportunity sampling:

Answer 30

• less representative than other methods, as it only reflects those who are in the same vicinity as the researcher when they sought the ppts - will only reflect members of the research who were present at the time -> findings less generalisable
• the sample may be biased as investigator has full control over who they choose to be part of the sample -may pick ppts they think will support their hypothesis - decrease in validity

Question 31

What is volunteer sampling:

Answer 31

1. researcher will advertise the opportunity to take part in the study on relevant websites/ newspapers and appropriate locations
2. upon seeing the advertisement, ppts themselves contact the researcher if they are interested
3. those who contact the researcher then form the sample

Question 32

Strength of volunteer sampling:

Answer 32

+ relatively quick and easy method of sampling compared to other methods such as “stratified sampling” as it does not require a lot of initial work (e.g collected names for all members of the target pop)

Question 33

Weaknesses of volunteer sampling:

Answer 33

• sample may attract atypical respondants - only those interested in the study’s aim will offer to take part in the study. This may lead to atypical results which cannot be generalised to the target population
• results may not be generalisable based on where the researcher advertises. e.g. if the study was advetised in the local newspaper, it will only lead to ppts from that local vicinity - thus sample is not representative + findings cannot be generalised by the target pop

Question 34

What is random sampling:

Answer 34

1. Researcher gathers names of all members of the target population and puts them in a hat
2. researcher then randomly picks names out of a hat (as many ppts one requires)
3. all names picked out will form the sample

Question 35

Strengths of random sampling:

Answer 35

+ no researcher bias as researcher cannot personally pick ppts they would like to take part in the study -> no control of who the randomly chosen ppts are going to be - cannot choose those who they think will supprt this hypothesis
+ no investigator effects

Question 36

Weaknesses of random sampling:

Answer 36

• requires gathering the names of all members of the target population - time consuming and inconvenient
• it is possible that by chance every ppt picked may be a specific type of ppt (e.g. every name picked out of hat is male) - therefore, sample may not be representative of the target population

Question 37

What is systematic sampling:

Answer 37

1. Collect a list of names (put them in order) from everyone in the target population (vs alphabetically)
2. generate nth trm by calculating: target pop/ sample size
3. select every nth person until sample size is reached
4. decide a starting point on list from which to begin collecting ppts by using a random no. generator to select a number from 1-5
5. researcher begins selecting ppts from number generated
6. find person with correlating number
7. researcher will then go through list from that individual and then select every nth person of target population - done until sample size is reached

Question 38

Strength of systematic sampling:

Answer 38

+ no researcher bias as researcher cannot personally pick ppts they would like to take part in the study

Question 39

Weaknesses of systematic sampling:

Answer 39

• requires gathering the names of all members of the target population - time consuming and inconvenient
• it is possible that by chance every ppt picked may be a specific type of ppt (e.g. every nth member selected from the list is male)

Question 40

What is stratified sampling:

Answer 40

1. researcher works out the proportion of groups in target population
2. researcher then tries to replicate these proportions within the sample (e.g if 60% of target population is female, then 60/100 ppts in the sample will be female)
3. to do this, researcher will gather the names of all members of target population and split them into groups (e.g all female names go into one hat)
4. the researcher will then randomly pick out however many ppts they require from each hat (e.g 60 from female hat, 40 for male hat)

Question 41

Strength of stratified sampling:

Answer 41

+ it is the only sampling technique which produces a truly representative sample which accurately reflects the composition of the target population -> as a result, any findings from such a sample will be generalised to the target population

Question 42

Weaknesses of stratified sampling:

Answer 42

• calcuating proportions of groups within the target population can be very time consuming
• finding ppts in line with the generated proportions may be problematic if the proportion is small + thus ppts are difficult to get hold of

Question 43

How can sampling lead to BIAS:

Answer 43

Some types of sampling allows the researcher influence over who partakes in research - lead to bias as researcher may pick people they know/ people from a particular group they prefer-> making sample unrepresentative, thus findings cannot be generalised-> lack validity

Question 44

What are pilot studies:

Answer 44

A small scale trial run of a study using a small group of ppts taken from a target population

Question 45

What do pilot studies aim to do:

Answer 45

Aim to improve the quality of the research (e.g. remove potential extraneous variables) + help avoid unneccessary work and save money and time.
- For example: to test the standardised instructions are clear, appropriate language is used and test timings of tasks.
- does not tell us anything about research