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© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Chapter 5 Making Systematic Observations
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Factors Affecting Your Choice of Variables to Manipulate or Observe Research Tradition Your variables may be similar to those included in previous studies You may use previously used dependent variables while manipulating new independent variables Theory A theory on which you are relying may suggest certain variables to be included
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Availability of New Techniques Sometimes a new technique is developed, allowing you to observe a variable that previously could not be observed Availability of Equipment The variables you manipulate or observe may be limited by the equipment available to you
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Factors Affecting Your Choice of Measures The RELIABILITY of a Measure A reliable measure produces similar results when repeated measurements are made under identical conditions Reliability can be established in several ways Test-retest reliability: Administer the same test twice Parallel-forms reliability: Alternate forms of the same test used Split-half reliability: Parallel forms are included on one test and later separated for comparison
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. ACCURACY of a Measure An accurate measure produces results that agree with a known standard A measurement instrument can be inaccurate but reliable The reverse cannot be true In psychology, standards are rare so accuracy may not be possible to establish Standardization uses average within a population
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. The VALIDITY of a Measure A valid measure measures what you intend it to measure Most important when using psychological tests (e.g., IQ test) Validity can be established in a variety of ways Face validity: Assessment of adequacy of content. Least powerful method Content validity: How adequately does a test sample behavior it is intended to measure?
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Criterion-related validity: How adequately does a test score match some criterion score? Takes two forms Concurrent validity: Does test score correlate highly with score from a measure with known validity? Predictive validity: Does test predict behavior known to be associated with the behavior being measured? Construct validity: Do the results of a test correlate with what is theoretically known about the construct being evaluated?
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Using Established Versus New Measures You need not spend time assessing validity and reliability of established measures However, they may not meet your research needs New measures must be evaluated for validity and reliability, which takes time and effort However, they may better meet your research needs
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Scales of Measurement Nominal Scale Lowest scale of measurement involving variables whose values differ by category (e.g., male/female) Values of variables have different names, but no ordering of values is implied Ordinal Scale Higher scale of measurement than nominal scale Different values of a variable can be ranked according to quantity (e.g., high, moderate, or low self-esteem)
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Interval Scale Scale of measurement on which the spacing between values is known (e.g., rating a book on a scale ranging from 0 to 10) No true zero point Ratio Scale Similar to interval scale, but with a true zero point (e.g., number of lever presses)
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Factors Affecting Your Choice of a Scale of Measurement Information Yielded A nominal scale yields the least information. An ordinal scale adds some crude information. Interval and ratio scales yield the most information. Statistical Tests Available The statistical tests available for nominal and ordinal data (nonparametric) are less powerful than those available for interval and ratio data (parametric) Use the scale that allows you to use the most powerful statistical test
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Ecological Validity Sometimes your research requires you to use a measure that reflects what people do in the real world (e.g., a nominal guilty/not guilty verdict) Such scales have ECOLOGICAL VALIDITY When necessary, choose an ecologically valid measure, even if it means loss of information You can always include another scale to gain more information
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Adequacy of a Dependent Measure Adequacy of a dependent measure is related to the sensitivity of the measure and range effects Sensitivity Is a dependent measure sensitive enough to detect behavior change? An insensitive measure will not detect subtle behaviors
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Range Effects Occur when a dependent measure has an upper or lower limit Ceiling effect: When a dependent measure has an upper limit Floor effect: When a dependent measure has a lower limit. Affect data in two ways Limiting values of your highest or lowest data point Variability of scores within affected treatments is reduced May cause misleading results from statistical analysis of data
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Types of Dependent Variables Behavioral Measure Record actual behavior of subjects Several types Frequency: Count of the number of behaviors that occur Latency: The amount of time it takes for a behavior to occur Number of errors: The number of incorrect responses made May not allow you to determine the underlying cause for behavior
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Physiological Measure Physical measure of body function (e.g., EEG) Typically requires special equipment Most physiological measures are noninvasive Some require an invasive procedure (e.g., implanting an electrode in the brain of a rat) Allow you to make precise measurements of arousal of a subject’s body Must infer psychological states
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Self-Report Measure Participants report on their own behavior or state of mind A rating scale is a commonly used self-report measure E.g., rate the attractiveness of a person on a 0 to 10 scale Q-sort methodology is another popular self-report measure Self-report measures are popular and easy to use, but may have questionable reliability and validity You cannot be sure that a participant is telling you the truth when using a self-report measure
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Reactivity in Psychological Research A psychological study is a social situation A participant’s social history can affect how he or she responds to a study You should not assume that your participant is a passive recipient of the parameters of your study Simply observing someone changes his or her behavior A problem in human and animal research
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Demand Characteristics Cues provided by the researcher and the research context that give participants information about a study The cues focused on by the participant may not be relevant to your study and can adversely affect results
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Role attitude cues (attitude adopted by a participant) can affect outcome of a study Cooperative attitude: Participant wants to help researcher Defensive or apprehensive attitude: Participant is suspicious of experimenter and situation Negative attitude: Participant motivated to ruin a study
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Experimenter Effects An experimenter can unintentionally affect how a participant behaves in a study Experimenter bias occurs when the experimenter’s behavior influences a participant’s behavior Two sources of experimenter bias Expectancy effects: When an experimenter expects certain types of behavior from participants Treating different groups differently: Treating participants differently, depending on the condition to which they were assigned
© 2005 The McGraw-Hill Companies, Inc., All Rights Reserved. Experimenter bias affects internal and external validity Steps must be taken to reduce experimenter bias Use a blind technique where the experimenter does not know the condition to which a participant has been assigned Use a double-blind technique where neither the experimenter nor participant knows the condition to which a participant has been assigned Automate the experiment
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