Research Methods: Chapter 10 - 12

• An experiment means that the researchers manipulated at least one variable and measured another variable
• A manipulated variable is a variable that is controlled, such as when the researchers assign participants to a particular level of the variable
• Measured Variables take the form of records of behavior or attitudes, such as self-reports, behavioral observations, or physiological measures
• In an experiment, the manipulated (causal) variable is the independent variable
• Conditions are levels of independent variables
• The measured variable is called the dependent or outcome variable
• A control variable is any variable that an experimenter holds constant on purpose
• The causal criteria to make a causal claim are:

  1. Covariance
  2. Temporal Precedence
  3. Internal Validity
• A comparison group is a group in an experiment whose levels on the independent variable differ from those of the treatment group in some intended and meaningful way
• A control group is a level of an independent variable that is intended to represent "no treatment" or a neutral condition
• A treatment group is the other level of the independent variable
• A placebo group is a control group that is exposed to an inert treatment such as a sugar pill
• A design confound is a third variable that varies systematically with the independent variables and provides an alternate explanation for results
• A selection effect is where participants at one level of the independent variable are systematically different than participants at other levels of independent variables
• A solution to selection effect is random assignment and matched groups
• Independent-Groups Design: separate groups of participants are placed into different levels of the independent variable
• Within-Groups Design: each person is presented with all levels of the independent variable
• Posttest-Only Design: participants are randomly assigned to independent variable groups and are tested on the dependent variable once
• Pretest/Posttest Design: participants are randomly assigned to at least two groups and are tested on the key dependent variable twice
• Repeated-Measures Design: participants are measured on a dependent variable more than once, after exposure to each level of the independent variable
• Concurrent-Measures Design: participants are exposed to all the levels of an independent variable at roughly the same time, and a single attitudinal preference is the dependent variable
• Advantages of Within-Group Design:

  • participants in groups are equivalent because they are the same/serve their own controls
  • gives researchers more power to notice differences between conditions
  • requires fewer participants
• Order Effects occur when being exposed to one condition affects how participants respond to other conditions
• Counterbalancing is when researchers present the levels of the independent variable to participants in different sequences
• 2 Types of Counterbalancing:

  1. Full Counterbalancing: all possible condition orders are represented
  2. Partial Counterbalancing: only some of the possible condition orders are represented
• Disadvantage of Within-Group Design:

  • potential of order effects
  • may not be practical or possible
  • Demand Characteristics: could experiencing all levels of IV change the way participants act?
• A manipulation check is an extra dependent variable that researchers can insert into an experiment to convince them that their experimental manipulation worked

  They also check for floor and ceiling effects and weak manipulations
• A pilot study is a simple study using a separate group of participants that is completed before the study of primary interest to confirm the effectiveness of the manipulations
• Cohen's d is the statistic that reflects effect size of two groups
• A maturation threat is a change in behavior that emerges more or less spontaneously over time
• A history threat is a result of a historical or external factor that systematically affects most members of the treatment group
• Regression Threat/Regression to the mean: if a group average is unusually extreme at time 1, the next time it is measured it will be less extreme
• An attrition threat is a reduction in participant numbers if the likelihood of dropping out differs systematically
• Testing threat is a change in participants as a result of taking a test more than once
• Instrumentation Threats occur when a measuring instrument changes over time
• A selection-history threat is an outside event or factor that affect those at one level of the independent variable
• In a selection-attrition threat, only one of the experimental groups experience attrition
• Observer bias occurs when researchers' expectations influence their interpretation of the results
• Observer bias threatens internal and construct validity
• Demand Characteristics are when participants guess what the study is about and change their behavior in the expected direction