Scientific Methods in Psychology

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Scientific Methods in Psychology
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The Scientific Method

• Science is a word derived from Latin roots
  scientia meaning knowledge.
• Why do we need it?
• scientific method provides guidelines for
  scientists in all fields to use in evaluating
  hypotheses and broader theories

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Scientific Theories

• What is a theory?
• A theory is a comprehensive explanation of
  observable events and conditions.

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The Scientific Method

• How do we support claims scientifically?
• A hypothesis is a testable prediction of what
  will occur under a stated set of conditions.

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Figure 2.1

• Figure 2.1 A hypothesis leads to predictions. An
  experimental method tests those predictions a
  confirmation of a prediction supports the
  hypothesis a disconfirmation indicates a need to
  revise or discard the hypothesis. Conclusions
  remain tentative, especially after only one
  experiment. Most scientists avoid saying that
  their results prove a conclusion.

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The Scientific Method

• The importance of replication

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General Principles of Research

• Definitions of Psychological Terms
• The problems of measurement
• Need to measure the phenomena we are studying
• Sometimes what we study in psychology is not
  tangible

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General Principles of Research

• Definitions of Psychological Terms
• An operational definition is one that specifies
  the operations or procedures used to produce or
  measure something. Its a way to give an
  intangible idea a numerical value.

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General Principles of Research

• Population vs Samples

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General Principles of Research

• Samples
• A convenience sample is a group chosen because of
  its ease of availability and study.
• A representative sample closely resembles the
  population in terms of gender, ethnic or racial
  groups, age levels, other characteristics might
  have some relevance to the results.

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General Principles of Research

• Population Samples
• random sample is one in which everyone in the
  population has equal chance of being selected.
• cross-cultural sample is one that contains groups
  of people from at least two distinct cultures.

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General Principles of Research

• Experimenter Bias
• tendency of experimenter to unintentionally
  distort procedures or results of an experiment
  based on the expected or desired outcome of the
  research.

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General Principles of Research

• Methods to counteract Experimenter Bias
• Using blind observers who record data without
  knowing what the researcher is studying.
• Using a placebo control. A placebo is a sham
  treatment that makes it very difficult for the
  subjects (single-blind) or the subjects and
  experimenter (double-blind) to know who has
  received the treatment and who has not.

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General Principles of Research

• Research Design
• There are many methods used to study
  psychological concepts and phenomena.

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General Principles of Research

• Observational (non-experimental) Research Design
• Naturalistic Observation
• Careful monitoring and examination of what people
  and animals do under more or less natural
  circumstances.

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General Principles of Research

• Observational Research Design
• Case History
• A thorough observation and description of a
  single individual

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General Principles of Research

• Observational Research Design
• Survey
• A survey is a study of the prevalence of certain
  beliefs, attitudes, or behaviors, based on
  peoples responses to specific questions.

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General Principles of Research

• Correlational Studies
• Correlation
• Correlation is a measure of the relationship
  between two variables which are both outside of
  the investigators control.

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General Principles of Research

• Correlational Studies
• The value of the correlation coefficient can
  range from 1.00 to 1.00.
• The higher the absolute value, the stronger the
  relationship is, regardless of the direction.
• A negative correlation (-) means that as one
  variable increases, the other decreases.

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General Principles of Research

• Experiments
• Experiment
• A study in which the investigator manipulates at
  least one variable (independent) while measuring
  at least one other variable (dependent).

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General Principles of Research

• Experiments
• Other important terminology
• Experimental group
• Control group
• Random assignment

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General Principles of Research

• Possible problems in carrying out and
  interpreting the results of experiments
• Demand Characteristics Cues that tell a subject
  what is expected of him or her, and what the
  researcher hopes to find.

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General Principles of Research

• Possible problems in carrying out and
  interpreting the results of experiments
• Ethical Considerations Researchers must weigh
  possible harm and benefits

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General Principles of Research

• Safeguarding human subjects well-being
• Use of informed consent
• Institutional Research Board (IRB)

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Descriptive Statistics

• Descriptive statistics are mathematical summaries
  of results. There are two broad categories of
  descriptive statistics
• Measurements of central tendency
• Measurements of variation or dispersion

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Descriptive Statistics

• Measurements of Central Tendency
• The mode
• The Mean
• The Median

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Descriptive Statistics

• Measurements of Variation
• The range is a statement of the highest and
  lowest scores
• If our distribution has the following scores 1,
  2, 3, 5, 7, 9, 9, 10, the range is from 1 to 10.

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Descriptive Statistics

• Measurements of Variation
• standard deviation (SD) is a measurement of the
  amount of variation among scores in a normal
  distribution.

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 Figure 2.17

• Figure 2.17  In a normal distribution of scores,
  the amount of variation from the mean can be
  measured in standard deviations. In this example
  scores between 400 and 600 are said to be within
  1 standard deviation from the mean scores
  between 300 and 700 are within 2 standard
  deviations.

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Evaluating Results Inferential Statistics

• Probability Values
• A probability value is a way to estimate if a
  score would be extremely rare given what we know
  about the likely range in which the population
  mean falls.
• If there is a 95 certainty that the population
  mean falls between 5.0 and 7.0, and a score falls
  at 8.2, then that score has a probability value
  of less than 5 (p lt .05) and it is an
  exceptional score in some way.

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Evaluating Results Inferential Statistics

• Probability Values and Statistical Significance
• scores that are exceptional are interpreted as
  being unlikely to have arisen by chance.
• A result that is unlikely to have occurred by
  chance in a distribution is interpreted as being
  statistically significant.