Experiments

• Laboratory = involves manipulation of an independent variable under controlled conditions, positives are that it is highly controlled and easy to replicate however it lacks ecological validity and is more likely to show demand characteristics 
• Natural/quasi = the Independent variable is naturally occurring such as gender, age or even, positives are that there is less bias sample and it is a naturally occurring IV, negatives are that it is hardly to replicate and that there is less control over the variables 
• Field = an experiment in a natural setting which still includes the manipulation of an IV, positives are that it has high ecological validity and that there is less bias sampling however it lacks control and it difficult to replicate

   
• Extraneous variables = something that is not under control in the experiment that could influence the results
• Confounding variable = something that could distort the findings and spoil the experiment 
• One-tailed directional = always predicts a difference or change between groups and has a lot of previous research behind it
• Two-tailed directional = always predicts a difference or change between groups however has very little or no previous research behind it
• Null hypothesis = always predicts that there will be no difference or change between the groups

   
• Independent measures design = each participant only takes part in one part of the study, positives are that there is less demand characteristics and no issue of order effects but negatives are that more participants are needed and the results are harder to compare
• Repeated measures design = each participants takes part in both parts of the study, positives are that the results easy to compare and less participants are needed but negatives are that there are experimenter effects and more demand characteristics  
• Matched pairs design = participants are matched into pairs based on a variable that needs to be controlled and each person does each part of the study, positives are that there are less demand characteristics and no issue of order effects but negatives are that it takes longer as similar participants need to be found and if one participants drops out or withdraws their data then you lose both participants sets of data from your experiment
• opportunity = participants that are available at the time 
• Volunteer = participants select themselves to take part in the study
• Random = selects the participants randomly
• Stratified = selecting participants in proportion to how they occur within the target population
• Unsolicited = participants are unaware they are taking part in the study
• Systematic = e.g. Visit an area of the target population and every nth person is selected to take part
• Snowball = chain referral