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Research Methods Chapter 2

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Reasoning Fallacies Hindsight bias – tendency to believe, after learning an outcome, that we would have foreseen it The “I knew it all along” phenomenon

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Psychology as Science Empiricism – belief that accurate knowledge of the world requires observation of it Limitations of casual observation: Unstable Can’t tell us about the properties we might be interested in

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Psychology as a Science -cont- So we must use measurement to: Define the property we want to measure in concrete terms Operational definition – description of procedures used to define research variables Ex: human intelligence may be operationally defined as what an intelligence test measures

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Psychology as a Science -cont- A good measurement has Validity – allows one to draw accurate inferences from it Replication– produces the same result whenever it is used to measure the same thing

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Case study Studying a single individual in depth

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Naturalistic observation Unobtrusively observing people in their natural environment Avoid demand characteristics – aspects that cause people to behave as they think an observer wants/expects them to behave Limitations: Some things psychologists want to observe don’t occur naturally Some things can only be gathered from direct observation with a person

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Survey Survey - uses a representative sample of people to estimate attitudes or reported behaviors of a whole population Limitation: Respondents may not answer honestly

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Survey -cont- Population - all the cases in a group being studied from which samples may be drawn Random sample - every member of a population has an equal chance of inclusion

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Correlational Studies Correlation – the “co-relationship” or pattern of co- variation between two variables Positive – two sets of variables go up or down together Negative – two sets of variables relate inversely

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Correlation vs. Causation Third-variable correlation – two variables may be correlated only because they are both caused by a third variable Correlation does not prove causation

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Correlation -cont- Illusory correlation: The perception of a relationship where none exists

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Experimentation Used to establish the casual relationship between variables Independent variable – variable that is manipulated Is “independent” of what the participant says/does Dependent variable – variable that is measured “Depends” on what the participant says or does Control group – group that does not receive the treatment Experimental group – group does receive the treatment

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Experimentation -cont- An experiment is internally valid when: An independent variable has been effectively manipulated A dependent variable has been measured in an unbiased way with a valid, powerful, and reliable measure A correlation has been observed between the independent and the dependent variable External validity – property of an experiment in which the IV and DV is operationally defined in a normal, typical, or realistic way

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Experimentation -cont- It is generally not feasible to use a random sample when conducting an experiment Experiments utilize Random assignment - assigning participants to experimental and control groups by chance Double blind procedure - neither the research participants nor the research staff know if participants received the treatment or a placebo - sugar pill Eliminates placebo effect - experimental results caused by expectations alone

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Measures of Central Tendency Mean – sum of a set of scores in a distribution divided by the number of scores Extreme scores have a greater impact on the mean than on the mode or median Median – score that divides a frequency distribution exactly in half, so that the same number of scores lie on each side of it Mode – the most frequently occurring score in a distribution

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Measures of Variation Definition – a single score that presents information about the spread of scores in a distribution Range – the highest score in a distribution minus the lowest score Standard deviation – a standard measurement of how much the scores in a distribution deviate from the mean

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Normal distribution Form a bell-shaped curve In a normal distribution of test scores, 50% of scores fall at or above the mean score and 50% of scores fall at or below the mean score Approximately 1/3 of the scores fall one standard deviation below the mean and 1/3 fall one standard deviation above the mean

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All score-based normal curves have the following rule in common: Approximately 68% of all scores fall within one standard deviation of the mean Approximately 95% fall within two standard deviations of the mean Approximately 99.7% fall within three standard deviations of the mean

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Skewed distributions Positively skewed distributions have more scores on the low end of the scale The median is the best representation of central tendency Negatively skewed distributions have more scores on the high end of the scale The median is a better representative of central tendency

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Ethics 1.Obtain informed consent – written agreement to participate in a study made by an adult who has been informed of all the risks participation may entail 2.Participation may not be coerced 3.Psychologists must protect participants from physical or psychological harm 4.Risk of embarrassment or minor pain must be outweighed by social benefits of new knowledge gained by study 5.Must provide a debriefing – verbal description of true nature and purpose of study

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