Experiments: Types of Experiment (AQA GCSE Psychology)

A lab experiment is a research method in which the researcher can exert high levels of control over what happens as part of the experimental process

The researcher controls the environmental factors, such as noise and temperature (possible extraneous variables) so that the effects of the independent variable (IV) upon the dependent variable (DV) can be observed and measured

Lab experiments use a standardised procedure for example:

• The same number of participants take part in each condition of the IV

• Each participant is given the same instructions (apart from instructions regarding the task as this will differ per condition as per the IV)

• The same task/materials are used as far as possible given the IV

• Participants are given the same amount of time to complete the task per condition and across conditions if the IV allows it

All variables are kept the same/constant; only the independent variable changes between conditions

Keeping all variables constant means the DV can be measured exactly using quantitative data

Due to the high control involved, lab experiments go some way towards establishing a cause-effect relationship

The use of a standardised procedure ensures replicability and reliability

Demand characteristics may be an issue if participants guess the aim of the study or behave in ways which are self-conscious and unnatural

Lab experiments lack validity as they usually involve participants performing artificial tasks

A field experiment is a research method which takes place in a natural setting, away from the lab

The researcher has less control over what happens as part of the experimental process

The researcher controls the environment to some extent but they have to allow the fact that many extraneous variables are included in field experiments

Field experiments still involve the implementation of an IV and DV, for example:

• A confederate of the researcher pretends to collapse on a subway train:

  • The IV is whether the victim appears to be drunk or disabled

  • The DV is the number of people who go to the victim’s aid

• A researcher implements a ‘Kindness’ programme with half of the Year 5 students in a primary school:

  • The IV is whether the students have followed the ‘Kindness’ programme or not

  • The DV is the score they achieve on a questionnaire about prosocial behaviour after one month

Field experiments collect quantitative data but there is also more scope for researchers to obtain qualitative data as part of the research process, for example:

• Interviews with passengers who witnessed the ‘victim’ collapsing on the train

• Teachers’ observations of behavioural differences in the ‘Kindness’ programme children across the month of the study

Any qualitative data collected could be used to comment on the quantitative findings and shed light on the actions of the participants

Field experiments are high in ecological validity as they take place in real settings, often without people realising that they are taking part in the research

As people may not know they are being tested/observed they will not succumb to demand characteristics

The lack of control available to the researcher means that field experiments are lower in reliability than lab experiments

There are ethical issues if a field experiment does not gain informed consent or offer the right to withdraw to participants, plus there is the possible harm that the procedure may inflict on participants

A natural experiment is a research method which does not manipulate the IV, it uses naturally occurring phenomena, for example:

• Age e.g. an experiment in which digit-span recall is tested between a group of young people compared to a group of older people

• Gender/sex e.g. the performance of girls is compared to the performance of boys in an experiment testing emotional intelligence

• Circumstances e.g. a group of teachers from one school who have received training in empathy are compared to a group of teachers from another school who have not had this training on a task involving correctly identifying emotional states

The researcher has less control over what happens as part of the experimental process as they cannot randomly allocate participants to condition (the participants are the conditions e.g. either young/old, trained/untrained)

Natural experiments collect quantitative data

Natural experiments allow researchers to investigate topics/issues that would, otherwise be unethical to manipulate e.g. measuring the cognitive skills of adopted Romanian orphans compared to non-adopted UK children of the same age 

Natural experiments have good validity as they measure variables which are liable to change anyway

It is difficult to establish a cause-effect relationship due to the unknown nature of the naturally occurring variable e.g. ‘gender’ as an IV includes a whole range of other, related variables which are impossible to know and to control

Replicating natural experiments is problematic as the IV is the participants - and people cannot be replicated!