Experimental Methods

• Null hypothesis

  States there is no cause and effect between the two variables

  so results are due to chance

  serotonin levels have no effect on ability to cope with stress
• Alternative hypothesis

  there is a cause and effect between the two variables being studies

  results are not due to chance

  Alcohol with increase reaction times
• One tailed (directional hypothesis)

  Predicts the nature of the effect of the independent variable on dependent variable

  Adults will correctly recall more words than children
• Two tailed (non-directional hypothesis)

  Predicts that the independent variable will have an effect on the dependent variable, but the direction is not specified

  There will be a difference in how many correct recalled words by children and adults
• Laboratory experiment

  In a controlled artificial setting and manipulation of an independent variable and measure of dependent variable. Includes standardised procedures
• +/- of Laboratory experiment

  +is easy to replicate due to standardised procedures

  +allow for precise control of extraneous and independent variables which allows cause and effect to be established

  -the artificial setting can cause unnatural behaviour. low ecological validity

  -demand characteristics or experimenter effects can cause bias and become confounding variables
• Field Experiment

  Are done in everyday environments but there is still a manipulation of independent variables
• +/- of field experiment

  +higher mundane realism as in a less artificial setting

  +Reduce demand characteristics as aims are less apparent

  -harder to control extraneous variables as in a natural setting so does not have total control

  -harder to replicate
• Quasi experiment

  Conducted in everyday environments where the independent variable is naturally occurring so the experimenter has no control
• +/- of Quasi experiment

  +Fewer demand characteristics and participant effects

  +higher mundane realism and allows phenomena's which would be unethical to be studied

  -as the independent variable is not being directly manipulated we cannot draw definite conclusions of cause and effect

  -Extraneous variables cannot be controlled

  -replication is difficult/impossible
• Repeated measures design

  Involves using the same participants in each condition of the experiment
• +/- of repeated measures design

  +participant variables which could become extraneous variables are kept constant

  +fewer participants are required so is more economical

  -order effects such as fatigue and learning may become errors as participants figure out the aims which effect results

  -demand characteristics may become a problem as they do both conditions so may guess the aims
• Independent measures design

  involves using different participants for each condition of the experiement
• +/- of independent measures design

  +order effects do not influence second condition

  +demand characteristics are less of a problem as only in one condition

  -participant variables differ which could act as an extraneous variable such as age and gender

  -more participants are needed so is less economical
• Matched pairs design

  involves using different but similar participants in each condition.

  participants are matched on characteristics such as age, gender and IQ
• +/- of matched pairs design

  +participant variables are kept more constant

  +order effects do not occur as only in one condition

  +demand characteristics are less of a problem

  -participant variables cannot be perfectly matched

  -matching participants is time consuming and difficult

  -more participants are required so is less economical
• Pilot study

  is an initial run through of the procedure by selecting a few participants to try out the study on to identify any flaws

  It can help researchers spot an ambiguities or confusion in information

  Can stop floor or ceiling effect if task is too hard or easy
• Experiments study

  Independent variable = related or unrelated images

  Dependent variable = how many images remembered

  Repeated measures design

  We gathered 11 participants from the communal area who were willing to take part

  Each participant was shown a slide with 16 unrelated images for 30 seconds

  After this they were told to write down how many they remember

  This was them repeated for related images such as occupation