Independent and Dependent Variable

• In a psychology experiment, we first manipulate the antecedent conditions to create at least two different treatment conditions.
• When conducted skillfully, an experiment allows us to make cause-and-effect statements about behavior.
• Why “at least two?” Because in other experiments, we may have more than two groups with different levels of independent variables.
• The independent variable (IV) is the dimension that an experimenter intentionally manipulates; it is the antecedent the experimenter chooses to vary. This variable is "independent" in the sense that its values are created by the experimenter and are not affected by anything else that happens in the experiment.
• Independent variables are sometimes aspects of the physical environment that can be brought under the experimenter's direct control.
• Sometimes, experimenters manipulate experimental conditions so that subjects experience different psychological states: anxious versus non-anxious, happy versus sad, succeeding versus failing-psychological states can be independent variables. Or experimenters may use different sets of instructions as independent variables, such as instructing subjects to pay attention to the red circles or to the blue squares.
• The list of potential independent variables is endless
• To meet the definition of an experiment, at least two different treatment conditions are required; thus, an IV must be given at least two possible values in every experiment.
• The researcher decides which values of the IV to use. These values are called the levels of the independent variable in the experiment.
• The researcher varies the levels of the IV by creating different treatment conditions within the experiment.
• Each treatment condition represents one level of the IV. If the IV is to have two levels, there must be two different treatment conditions; if three values of the IV are to be used, there must be three different treatment conditions, and so on.
• In an ex post facto study, the researcher can explore the way behavior changes as a function of changes in variables outside the researcher's control.
• These are typically subject variables, characteristics of the subjects themselves (age, personality characteristics, gender, and so on) that cannot be manipulated experimentally.
• Although the researcher does not manipulate them, quasi-experimental variables are often independent in the sense that the researcher selects the particular values that will be included in the study.
• In quasi-experiments, the researcher selects rather than creates the levels of the IV by assigning subjects to treatment groups on the basis of a subject variable.
• In a true experiment, we test the effects of a manipulated independent variable--not the effects of different kinds of subjects.
• To guard against systematic differences in people in our treatment groups, we randomly assign subjects to receive different treatments.
• The dependent variable (DV) is the particular behavior we expect to change because of our experimental treatment; it is the outcome we are trying to explain.
• Because we manipulate the IV and measure its effects on the DV, dependent variables are sometimes called dependent measures.
• The dependent variable is dependent in the sense that its values are assumed to depend on the values of the independent variable
• If we expect to understand the causes of behavior, we need to focus on the relevant antecedent variables.
• Is the material going to be studied in the sample experiment considered an independent variable? No. The independent variable in the experiment is one that changes in levels or values to determine whether it has an effect to the dependent variable.
• You can have more than one independent variable. The simplest experiments will have one independent and one dependent variable but you can have two or more.
• An operational definition specifies the precise meaning of a variable within an experiment: It defines a variable terms of observable operations, procedures, and measurements.
• Operational definitions are quite different from ordinary dictionary definitions. A dictionary may define retention as “the fact of keeping something in one's memory”. Although the definitions might be adequate for everyday use, it is insufficient in the context of an experiment because they do not tell us how to produce different levels or values of the variables.
• Experimental operational definitions explain the precise meaning of the independent variables; these definitions describe exactly what was done to create the various treatment conditions of the experiment.
• Dependent variables are defined by measured operational definitions, which describe what we do to measure the variables.
• Extraneous variables are all variables, which are not the independent variable, but could affect the results of the experiment. Each poses special problems in an experiment.
• To make sure that an extraneous variable does not affect an experiment, sometimes we just take it out-we eliminate it.
• Ideally, we would like to eliminate all extraneous variables from an experiment, but this is easier said than done. Sometimes there is no quiet location.
• Factors such as the weather, the lighting, and the paint on the walls are simply there; we cannot eliminate them. Instead, we use the second control procedure constancy of conditions.
• Constancy of conditions simply means that we keep all aspects of the treatment conditions as nearly similar as possible. If we cannot eliminate an extraneous variable, we try to make sure that it stays the same in all treatment conditions (sana all di nagbabago).
• Balancing means distributing the effects of an extraneous variable across the different treatment conditions of the experiment.
• By using balancing, the study would have internal validity and greater external validity
• Do not sacrifice internal validity for external validity because internal validity is more important. You cannot have external validity unless a study, first, has internal validity
• Demand characteristics are aspects of the experimental situation that demand that people behave in a particular way.
• An experimenter generally wants participants to be as naive as possible. They should understand the nature and purpose of the experiment but not the exact hypothesis. The reason for this is simple. If subjects know what we expect to find they might try to produce data that will support the hypothesis.
• If behavior changes simply because subjects think the researcher wants an experiment to turn out in a particular way, the experiment has not measured what it was intended to measure.
• A single-blind experiment, an experiment in which subjects do not know which treatment they are getting.
• We can disclose some but not all information about the experiment to subjects. We can disclose what is going to happen to them in the experiment we can also keep them fully informed about the purpose of the study