Types of Experiments
When beginning research, psychologists must decide on the type of experiment and the research design that they wish to investigate their chosen study.
Laboratory Experiments: conducted under highly controlled conditions.
Field Experiments: Carried out in 'the field'. Real world situation.
Quasi/Natural Experiment: Independent variable is not manipulated by the experimenter.
Strengths and weaknesses of experiments
Strength: 1) Manipulation of IV can indicate cause-affect-effect relationship. 2) Increases control and accurate measurement. Weakness: 1) Articificial conditions may produce unatural behaviour, research could lack ecological validity. 2) Total control over all variables.
Strength: 1) Greater ecological validity as surroundings are natural. 2) Less likelihood of demand characteristics. Weakness: 1) Difficulties in controlling the situation, more possibility of bias from extraneous variables. 2) Time consuming.
Strength: Greater ecological validity since the change in the IV is natural. Weakness: 1) Impossible to replicate exacty.2) Ethical issues of consent, deception, invasion of privacy etc.
Research Designs & Variables
Independent Measures: Two groups/conditions in an experiment consisting of different individuals.
Repeated Measures: Two groups/conditions in an experiment consisting of the same individuals.
Matched Pairs: Every participant matched in one group.
Independent Variable: Manipulated by researcher.
Dependent Variable: Measured by researcher.
Confounding Variable: Has unintentional effects on dependent variable.
Extraneous Variable 1: (Participant): Confounding effects from characteristics of the participant. e.g. Differences in age, gender, hunger etc. (Both 1+2 can affect the dependent variable in which you can control)
Extraneous Variable 2: (Situational): " " " " environmental characteristics. e.g. smell, temperature, sight etc.
Strengths & Weaknesses of Research Design
Strengths: Participants only have to it once, not likely to be bored or work out what's being tested. Affects their behaviour. Weaknesses: As there's different participants in groups, they'll have differences between them.
Strengths: Participants are in same groups so its easier to compare their performance in each condition. Weaknesses: Either the participants will do the same task twice, which may lead to boredom or improvement and may help them work out what's being tested.
Strengths: 1) Participants only have to be tested once. 2) Differences between the two groups have been reduced. Weaknesses: Lengthy and time consuming process that can be qutie 'wasteful' of participants as a large number of people would need to find appropriate pairs.
Alternate Hypothesis: Statement to be tested, predicts there will be a relationship between two variables or a difference between two conditions. E.g. Lack of sleep makes you eat more.
Null Hypothesis: Statement stating there will be NO significant difference/relation between two variables or conditons. E.g. There will be no relationship between eating more from lack of sleep.
One-Tailed Hypothesis: Predicts the direction of the difference or predicts either positive or negative correlation will occur. E.g. There will be a relationship between eating and sleeping.
Two-Tailed Hypothesis: Predicts a difference between two variables but not the direction or in terms of correlational analysis it does not predict either a positive or negative correlation. E.g. Sleeping increase eating quality.
Ecological Validity: This type of validity refers to how well a study can be related to or reflects everyday real life. Reliability: Refers to the extent to which a meausre is repeated within itself.
Validity: Refers to whether a study measures or examines what it claims to measure or examine.
Demand Characteristics: Feature of an experiment (other than the IV) that influences a participant to try to guess what a study is about and look for clues as how to behave. It is any aspect of the study which has an influence on particpants to or answer what is expected of them.
Counterbalancing: Strategy often used when carrying out a consistent measures design to control for potentially confounding variables. (i.e order effects). Therefore counterbalancing involves alternating the order in which participants do the experiment.
Order Effects: Carrying out a repeated measures design it is possible that order effects such as practice effect or fatigue effect produce an unwanted effect.