1.2 Scientific Investigation Methodologies

A controlled experiment is a methodology used to test a hypothesis in which the researcher systematically manipulates (changes) one or more variables to investigate what effect these manipulations have on another variable.

A correlational study is a non-experimental study where the researcher investigates relationships between variables. Unlike in a controlled experiment, the researcher does not try to control or change any of the variables.

A correlation is a relationship or association between two variables in a data set. It is a measure of the strength and direction of the relationship between the two variables.

If two variables are correlated, there is a relationship between them, but does not mean that changes in the value of one variable causes changes in the value of the other variable.

e.g. a study finds a positive correlation between sleep duration and mood - does not necessarily mean that longer sleep causes better wellbeing, could be that people who get more sleep also have more structured routines in general and this could be the factor responsible for the correlation, rather than the sleep variable measured.

positive correlation – upwards

negative correlation – data slopes downwards

no correlation – scatterplots appear random

A case study is a detailed investigation of one instance of a broader phenomenon. A case study focuses on a particular person, activity, behaviour, event or problem in a real or hypothetical situation.

Advantage: the data is rich and highly detailed. A case study can include the complexities that are encountered in the real world.

Disadvantage: the information is specific to one particular case, many of the details may be specific to that single case and may not apply to the wider population or to other situations of interest.

Classification is a scientific activity that seeks to systematically organise phenomena, objects or events into manageable sets.

Identification is the process of recognising phenomena as belonging to particular sets or possibly being part of a new or unique set.

Fieldwork involves observing and interacting with a selected environment beyond the classroom or lab.

- used when researchers want to capture human thoughts, feelings and behaviours in a natural setting

- conducted through direct observation of behaviour or by using sampling methods to gather a group of people in a natural environment.

Modelling means creating a conceptual, mathematical or physical representation (that is, a model) of a system of concepts, events or processes


- models can be used to test hypotheses or to determine underlying mechanisms and processes in ways that may be unrealistic or even impossible to test with real people.

Product, process or system development is the design or evaluation of a process, system or artefact to meet a human need.

e.g. psychology-focused smartphone apps

A literature review is a report produced by reading scientific research on a particular area and writing a summary.