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Chapter Six: The Basics of Experimentation I: Variables and Control

Chapter Six: The Basics of Experimentation I: Variables and Control. The Nature of Variables. Variable. The Nature of Variables. Variable A variable is an event or behavior that can assume at least two values. Operationally Defining Variables.

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Chapter Six: The Basics of Experimentation I: Variables and Control

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  1. Chapter Six:The Basics of Experimentation I: Variables and Control

  2. The Nature of Variables • Variable

  3. The Nature of Variables • Variable • A variable is an event or behavior that can assume at least two values.

  4. Operationally Defining Variables • Bridgman (1927) suggested that researchers should define their variables in terms of the operations needed to produce them.

  5. Operationally Defining Variables • Bridgman (1927) suggested that researchers should define their variables in terms of the operations needed to produce them. • Such definitions allow others to replicate your research and arecalled operational definitions.

  6. Independent Variables • Independent Variables (IV’s)

  7. Independent Variables • Independent Variables (IV’s) • IV’s are those variables that the experimenter purposely manipulates.

  8. Independent Variables • Independent Variables (IV’s) • IV’s are those variables that the experimenter purposely manipulates. • The IV constitutes the reason the research is being conducted; the experimenter is interested in determining what effect the IV has.

  9. Types of IV’s • Physiological IV

  10. Types of IV’s • Physiological IV • The physiological state of the participant that the experimenter manipulates.

  11. Types of IV’s • Experience IV

  12. Types of IV’s • Experience IV • Manipulation of the amount or type of training or learning.

  13. Types of IV’s • Stimulus or environmental IV

  14. Types of IV’s • Stimulus or environmental IV • An aspect of the environment that the experimenter manipulates.

  15. Participant characteristics • Aspects of the participant, such as age, sex or personality traits, that are treated as if they are IV’s.

  16. Participant characteristics • Aspects of the participant, such as age, sex or personality traits, that are treated as if they are IV’s. • They are not IV’s because they cannot be manipulated by the experimenter.

  17. Extraneous Variables (confounders) • Extraneous variables

  18. Extraneous Variables (confounders) • Extraneous variables • Uncontrolled variables that can cause unintended changes between groups.

  19. Extraneous Variables (confounders) • Extraneous variables • Uncontrolled variables that can cause unintended changes between groups. • Confounding

  20. Extraneous Variables (confounders) • Extraneous variables • Uncontrolled variables that can cause unintended changes between groups. • Confounding • A situation in which the results of an experiment can be attributed to either the operation of an IV or an extraneous variable.

  21. Dependent Variables • Dependent Variable (DV)

  22. Dependent Variables • Dependent Variable (DV) • A response or behavior that is measured. It is desired that changes in the DV are directly related to manipulation of the IV.

  23. Recording or Measuring the DV • Correctness

  24. Recording or Measuring the DV • Correctness • Only correct responses are counted.

  25. Recording or Measuring the DV • Correctness • Rate or Frequency

  26. Recording or Measuring the DV • Correctness • Rate or Frequency • Rate of responding determines how rapidly responses are made during a specified time period.

  27. Recording or Measuring the DV • Correctness • Rate or Frequency • Rate of responding determines how rapidly responses are made during a specified time period. • The number of responses or events that occur within a specified time period is the frequency.

  28. Recording or Measuring the DV • Correctness • Rate or Frequency • Degree or Amount

  29. Recording or Measuring the DV • Correctness • Rate or Frequency • Degree or Amount • Latency or Duration

  30. Should You Record More than One DV? • If you have the measurement capabilities, there is nothing to prohibit the recording of more than one DV.

  31. Should You Record More than One DV? • If you have the measurement capabilities, there is nothing to prohibit the recording of more than one DV. • If recording an additional DV makes a meaningful contribution to your understanding of the phenomenon under study, then you should give it serious consideration.

  32. Characteristics of a Good DV • A DV is valid when it measures what the experimental hypothesis says it should measure.

  33. Characteristics of a Good DV • A DV is valid when it measures what the experimental hypothesis says it should measure. • A good DV must be directly related to the IV and must measure the effects of the IV manipulation as the experimental hypothesis predicts it will.

  34. Characteristics of a Good DV • A DV is valid when it measures what the experimental hypothesis says it should measure. • A good DV must be directly related to the IV and must measure the effects of the IV manipulation as the experimental hypothesis predicts it will. • A good DV is also reliable.

  35. Nuisance Variables • Nuisance Variables

  36. Nuisance Variables • Nuisance Variables • Unwanted variables that can cause the variability of scores within groups to increase.

  37. Nuisance Variables • Nuisance Variables • Unwanted variables that can cause the variability of scores within groups to increase. • Nuisance variables increase the spread of scores within a distribution; they do not cause a distribution to change its location.

  38. Controlling Extraneous Variables • The experimenter must exercise control over both extraneous variables and nuisance variables so the results of the experiment are as meaningful (no extraneous variables present) and clear (minimal influence of nuisance variables) as possible.

  39. Basic Control Techniques • Randomization

  40. Basic Control Techniques • Randomization • A control technique that ensures that each participant has an equal chance of being assigned to any group in an experiment.

  41. Basic Control Techniques • Randomization • Elimination

  42. Basic Control Techniques • Randomization • Elimination • A control technique whereby extraneous variables are completely removed from an experiment.

  43. Basic Control Techniques • Randomization • Elimination • Constancy

  44. Basic Control Techniques • Randomization • Elimination • Constancy • A control technique by which an extraneous variable is reduced to a single value that is experienced by all participants.

  45. Basic Control Techniques • Randomization • Elimination • Constancy • Balancing

  46. Basic Control Techniques • Randomization • Elimination • Constancy • Balancing • A control procedure that achieves group equality by distributing extraneous variables equally to all groups.

  47. Basic Control Techniques • Randomization • Elimination • Constancy • Balancing • Counterbalancing

  48. Basic Control Techniques • Randomization • Elimination • Constancy • Balancing • Counterbalancing • A procedure for controlling order effects by presenting different treatmentsequences.

  49. Basic Control Techniques • Randomization • Elimination • Constancy • Balancing • Counterbalancing

  50. Counterbalancing • Within-Subject counterbalancing

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