All experiments involve an IV (independent variable) and DV (dependent variable). This IV is varied in order to see how this affects the DV, thus demonstrating a causal relationship. As far as possible all other variables are controlled, so any changes in the DV are due to the IV rather than extraneous variables (EV's).
Lab experiments An experiment conducted in a controlled environment which therefore tends to be high in terms of internal validity because many EV's can be controlled - though some EVs (such as experimenter effects and demand characterisitics) may reduce internal validity. Control also increases replicability, which is desirable, but reduces external (ecological) validity because a highly controlled situation may be less like everyday life.
Field experiments An experiment conducted in a more natural environment but the experimenter still has control over the IV. It may be possible to control EV's, though such control is more difficult than in a lab experiment. Experimenter effects are reduced because participants are usually not aware of being in a study. However, demand characteristics may still be problematic, for example the way an IV is operationalised may convey the experimental hypothesis to participants.
Natural experiment An experiment that makes use of exisiting IVs, such as a treatment used for people with mental illness. Strictly speaking, an experiment involves the deliberate manipulation of an IV by an experimenter, so causal conclusions cannot be drawn from a natural experiment. In addition, participants are not randomly allocated to conditions in a natural experiment (which may reduce validity) but it is often the only way to study certain behaviours or experiences, such as the effects of a poor diet on intellectual development.
Questionnaires and Interviews
Psychologists use questionnaires and interviews to find out what people think and feel. Interviews are essentially real-time, face-to-face (or over the phone) questionnaires, although in an interview where the questions are developed by the interviewer as a response to the answers given by the interviewee.
Advantages and diadvantages Questionnaires/structured interviews can be more easily repeated than unstructured interviews, which is an advantage. However, unstructured interviews may provide unexpected insights and…