- the psychological investigations exam
what are the key features of science ? in scientific enquiry there are four key features:
- theory: we start with an idea or hypothosis (prediction) about something
- empirical evidence: we need to carry out a study to provide objective evidence for the theory
- control: the study must be conducted under controlled conditions so that we can be sure that we are studying what we inended to study
- replication: if a study and the theory it supports is to be true (valid), then it must be shown to be replicable
experiments must have key features which include:
- the effect of independent variable on dependent variabe is being tested
- controlled conditions are established
- replication of the procedures is possible, in order to test the reliability of the findings
all the extraneous variables that we want to control will fall into one of two categories:
- subject variabes or personal factors- these are factors within a person that can vary over time or vary with a situation eg tired at night, more awake during the day.
- situational variables or environmental factors- eg level of noise in a room
controlling situational variables or environmental factors
there are a number of stratergies for controlling extraneous environmental variables. these include standardisation, randomisation and counterbalancing.
- standardisation- means keeping the test conditions the same for every subject or participant. it is a method of controlling situational variables or environmntal factors which might have an influence on the subject or participants behaviour. to keep all extraneous variables constant across experimental conditions, researchers use standard apparatus, standard instructions and procedures and standard locations.
- randomisation- or random allocation, is where participants are allocated to experimental conditions on a chance basis, by drawing lots or tossing a coin.this is done to control extraneous variables. it can also be used to avoid experimental bias (whether concious or unconcious) when allocating participants to conditions for a study.
- counterbalancing- is a third technique for controlling situational factors such as time of day or location.
counterbalancing to control order effects
counterbalancing is a method of controlling variabes, especially order effects in repeated measures designs, by systematically varying the order of presentation of tasks to subjects or participants. so where one half of the subjects do one condition first, condition A followed by condition B, and the other half does the opposite, condition B followed by condition A, this is known as ABBA counterbalancing design.
controlling subject variables and personal factors (individual differences)
to control extraneous personal variables experimental designs can be used:
- repeated measures design
- matched subjects design
- independent groups design
these designs have two functions:
- to provide a way for experimenters to control extraneous subject variables and personal factors
- to provide experimental and control conditions for the experiment.
in a repeated measures design each subject is tested in every condition-thus each subject provides their own comparison (control) scores. a repeated measures design is therefore a related design as each pair of scores is form one participant.