Simply any investigative approach that does not qualify by definition as an experiment . An experiment is traditionally defined as a procedure when the investigator manipulates some aspect of a situation in order to observe the effects of that manipulation. In the absence of that manipulation an investigation would be considered to be ‘non-experimental’. Some types of experiment (such as natural experiments) do not have this direct manipulation as a feature, so are regarded as ‘ quasi-experiments ’. Examples of non-experimental approaches in psychology would include the observational method and case studies . Arguments about which method is best, experimental or non-experimental, are pretty futile, as each offers different advantages to the researcher. Experiments generally offer greater control and an ability to make statements about cause and effect. Non-experimental methods, on the other hand, tend to offer insights derived from more life-like situations, and therefore tend to have a greater ecological validity . Non-experimental approaches to research are best seen as one of a range of investigative tools that are available to the research psychologist.