The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Chapter Six: The Basics of Experimentation I: Variables and Control Chapter Six:

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The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Chapter Six: The Basics of Experimentation I: Variables and Control Chapter Six: The Basics of Experimentation I: Variables and Control

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education The Nature of Variables Variable A variable is an event or behavior that can assume at least two values. 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 are called operational definitions.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Independent Variables Independent Variables (IVs)

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Independent Variables Independent Variables (IVs) IVs are those variables that the experimenter purposely manipulates.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Independent Variables Independent Variables (IVs) IVs 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Types of IVs Physiological IV The physiological state of the participant that the experimenter manipulates. Experience IV Manipulation of the amount or type of training or learning. Stimulus or environmental IV An aspect of the environment that the experimenter manipulates.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Participant characteristics Aspects of the participant, such as age, sex or personality traits, that are treated as if they are IVs. They are not IVs because they cannot be manipulated by the experimenter.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Extraneous Variables (confounders) Extraneous Variables

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Extraneous Variables (confounders) Extraneous variables Uncontrolled Variables that can cause unintended changes between groups.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Extraneous Variables (confounders) Extraneous variables Uncontrolled Variables that can cause unintended changes between groups. Confounding

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Dependent Variables Dependent Variable (DV)

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness Only correct responses are counted.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness Rate or Frequency

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness Rate or Frequency Rate of responding determines how rapidly responses are made during a specified time period.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness Rate or Frequency Degree or Amount

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording or Measuring the DV Correctness Rate or Frequency Degree or Amount Latency or Duration

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Recording More than One DV If you have the measurement capabilities, there is nothing to prohibit the recording of more than one DV.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Characteristics of a Good DV A DV is valid when it measures what the experimental hypothesis says it should measure.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Nuisance Variables

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Nuisance Variables Unwanted variables that can cause the variability of scores within groups to increase.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination A control technique whereby extraneous variables are completely removed from an experiment.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education 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.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy Balancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy Balancing A control procedure that achieves group equality by distributing extraneous variables equally to all groups.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy Balancing Counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy Balancing Counterbalancing A procedure for controlling order effects by presenting different treatment sequences.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Basic Control Techniques Randomization Elimination Constancy Balancing Counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Presentation of different treatment sequences to the same participant.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Presentation of different treatment sequences to the same participant. Within-Group counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Group counterbalancing Presentation of different treatment sequences to different participants. Three basic requirements:

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Group counterbalancing Presentation of different treatment sequences to different participants. Three basic requirements: Each treatment must be presented to each participant an equal number of times.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Group counterbalancing Presentation of different treatment sequences to different participants. Three basic requirements: Each treatment must be presented to each participant an equal number of times. Each treatment must occur an equal number of times at each testing or practice session.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Group counterbalancing Presentation of different treatment sequences to different participants. Three basic requirements: Each treatment must be presented to each participant an equal number of times. Each treatment must occur an equal number of times at each testing or practice session. Each treatment must precede and follow each of the other treatments an equal number of times.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Within-Group counterbalancing Complete counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Within-Group counterbalancing Complete counterbalancing All possible treatment sequences are presented.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Within-Group counterbalancing Complete counterbalancing All possible treatment sequences are presented. You can calculate the number of sequences by using the formula n! ( n factorial).

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Within-Group counterbalancing Complete counterbalancing Incomplete counterbalancing

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Within-Subject counterbalancing Within-Group counterbalancing Complete counterbalancing Incomplete counterbalancing Only a portion of all possible sequences are presented.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Sequence or Order Effects

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Sequence or Order Effects Sequence or order effects are produced by the participant’s being exposed to the sequential presentation of the treatments.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Sequence or Order Effects Sequence or order effects are produced by the participant’s being exposed to the sequential presentation of the treatments. The sequence or order effect depends on where in the sequential presentation of treatments the participant’s performance is evaluated, not which treatment is experienced.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Carryover Effects

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Carryover Effects The effects of one treatment persist or carry over and influence responses to the next treatment.

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Differential Carryover

The Psychologist as Detective, 4e by Smith/Davis © 2007 Pearson Education Counterbalancing Differential Carryover The response to one treatment depends on which treatment was administered previously.