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Psychological Experiment Requirements: Controlling Variables & Overcoming Limitations, Summaries of Experimental Design

The essential components of psychological experiments, including the need for a controlled environment, dependent and independent variables, manipulation, and measurement. It also explores problems with experiments, such as confounding variables, manipulating human subjects, and artificiality. Psychologists value experiments for their control over extraneous factors and efficiency, but acknowledge their limitations.

Typology: Summaries

2021/2022

Uploaded on 09/27/2022

zeb
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What do we need for an experiment?
An environment that we systematically
control and manipulate in order to
observe the effect of the manipulation
upon some behavior to answer a
specific question.
2
What do we need for an experiment?
Said another way, we need:
Dependent variable
Independent variable
3
What do we need for an experiment?
Dependent variable
Measurement made by the researcher
Time until someone sits down.
4
What do we need for an experiment?
Independent variable
Manipulation in the controlled environment
There must be a t least 2 levels of the manipulated
variable in order to mak e a comparison.
Differen t doses
repeated measures
Presenc e vs. absence of variable
Control vs e xperimental group
pf3
pf4
pf5

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1

What do we need for an experiment?

An environment that we systematically

control and manipulate in order to

observe the effect of the manipulation

upon some behavior to answer a

specific question.

2

What do we need for an experiment?

Said another way, we need:

  • Dependent variable
  • Independent variable 3

What do we need for an experiment?

  • Dependent variable
    • Measurement made by the researcher
      • Time until someone sits down. 4

What do we need for an experiment?

  • Independent variable
    • Manipulation in the controlled environment
    • There must be at least 2 levels of the manipulated variable in order to make a comparison. - Different doses - repeated measures - Presence vs. absence of variable - Control vs experimental group

5

What do we need for an experiment?

  • Control over irrelevant variables
    • Independent variables with no manipulation 6

Why do psychologists value

experiments so much?

  • Better control over extraneous environment
  • This control allows us to conclude that the

difference in the dependent variable was caused

by the change in the independent variable.

  • Draw conclusions carefully
    • Deaf fleas 7

Why do psychologists value

experiments so much?

  • Economy (Quick & Efficient)
    • Naturalistic observation requires a great deal of time (and patience) to wait for the desired behavior to occur - Low frequency behaviors - Relationship between heat and aggression in the Arctic. - Speech errors - May miss the behavior when it does finally occur 8

Some Problems with Experiments

  • Can’t control EVERYTHING
    • Not all variables can be controlled (especially if you don’t know about it)
    • Confounded variable
      • Two or more variables whose separate effects can not be isolated.
      • Teaching effectiveness example
        • Prof. X uses book A
        • Prof. Y uses book B

13

Some Problems with Experiments

• Humans are not inert “manipulable objects”

  • They seek meaning in everything they do
  • Experiments that treat humans as mechanistic objects provide results that are misleading. 14

Some Problems with Experiments

• Limited number of variables

manipulated through a limited range

  • This range may not reflect the range encountered in the real world. 15

Some Problems with Experiments

• Limited number of variables

manipulated through a limited range

  • We might control away an interesting

influence or effect.

  • Word Frequency and Word Duration in speech error analysis 16

Some Problems with Experiments

Experiments are artificial!

  • Participants respond to a stimulus on the basis of extremely limited information - Words not in sentence, Lexical decision task - Lines or letters, not people or car keys

17

Some Problems with Experiments

Experiments are artificial!

• Bear little resemblance to real life, so how

can we be sure that what we observe in an

experiment happens in real life?

18

Some Problems with Experiments

Experiments are artificial!

• They lack external validity!

  • Can’t generalize to other:
    • populations, settings, independent variables, dependent variables, etc. 19

Are these real “concerns”?

Experiments are not conducted to yield estimates or likelihood of behavior.

  • “Artificialness” gives us control allowing us to test causal hypotheses.
  • Does a change in X lead to a change in Y?
  • NOT: How often does Y happen when given X?
    • It’s a feature, not a bug! 20

What do experiments do?

They test the predictions of a theory/model.

The theory is supposed to generalize,

not the experiment!

25

Psychological research is interested in:

Lab is used when there is no

counterpart in the real world.

  • Psychophysical studies lead to understanding systems that operate in the real world - Dark adaptation 26

Note

There ARE situations in which generalizability

and subject representativeness IS important.

  • “Applied” research
  • Educational research
  • Agricultural research