MODULE 7

• In the simplest experiments, an experimental hypothesis states a potential relationship between two variables: If A occurs, then we expect B to follow. In an experiment, variables are measurable elements that can vary or take on different values along some dimension. To be more precise, the hypothesis expresses a potential relationship between two kinds of variables, the independent and the dependent variable.
• An experiment's independent variable (IV) is the dimension that the experimenter intentionally manipulates.
• It is the antecedent the experimenter chooses to vary.
• 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.
• 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.
• 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. Be careful not to confuse the levels of the IV with the IV itself.
• How will we know whether changes in the levels of the IV have altered behavior?

  We measure another variable, called the dependent variable, to determine whether the independent variable had an effect.
• The dependent variable (DV) is the particular behavior we expect to change because of our experimental treatment.
• The dependent variable is the outcome we are trying to explain. Sometimes it helps to think of it this way: In an experiment, we are testing the effects Of the IV on the DV. 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: As the IV changes value (as we look at behavior under different treatment conditions), we expect to see corresponding changes in the value of the DV.
• An operational definition specifies the precise meaning of a variable within an experiment.
• Operational definition


  This defines a variable in terms of observable operations, procedures, and measurements.
• It is called an operational definition because it clearly describes the operations involved in manipulating or measuring the variables in an experiment.
• Operational definitions are statements of operating procedures, sets of instructions that tell others how to carry out an experiment. These statements are essential because many variables of interest to psychologists cannot be observed directly, and operational definitions describe variables in terms of observable reality.
• We include operational definitions in written reports of experiments so that other researchers will understand exactly what was done and will be able to replicate it.
• Ordinary dictionary definitions do not give us procedures we could follow to make people feel anxious or nonanxious or to produce more or less learning. Similarly, they contain no information on how to measure or quantify the variables. How would we determine who has more anxiety or more learning? Operational definitions provide both of those types of information.
• 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.
• An experimental operational definition includes all the steps that were followed to set up each value of the independent variable.
• Dependent variables are defined by measured operational definitions, which describe what we do to measure the variables.
• Measured operational definitions of the dependent variable describe exactly what procedures we follow to assess the impact of different treatment conditions. These definitions include exact descriptions of the specific behaviors or responses recorded and explain how those responses are scored. If we are using scores on a standardized test to measure our dependent variable, we identify the test by name: "scores on the Culture Fair Intelligence Test," not simply "scores on an intelligence test."
• Hypothetical constructs or concepts are unseen processes postulated to explain behavior.
• Hypothetical constructs, that is, constructs that cannot be observed directly.
• Constructs definitions


  Internal attributes or characteristics that cannot be directly observed. These are useful for describing and explaining behavior.
• Operational definition


  Identifies the set of operations required to measure an external (observable) behavior. This uses the resulting measurements as both a definition and a measurement of a hypothetical construct.
• Researchers often formulate different definitions for the same construct variable when it is used in different experiments.
• Operational definition is equally important when we are working with variables that can be observe more directly.
• Nominal


  The simplest level; classifies items into two or more distinct categories that can be named (e.g., men or women; yes or no; low, moderate, or high anxiety).
• Ordinal


  The next level; the magnitude of each value is measured in the form of ranks (e.g., first, second, or third place; most preferred to least preferred).
• Interval


  Higher level; measures magnitude or quantitative size using measures with equal intervals between the values (e.g., a semantic differential scale, a Likert scale, a number scale from 1 to 7).
• Ratio


  Highest level; measures magnitude or quantitative size using measures with equal intervals between all values and a true zero point (e.g., height, weight, inches etc.).
• When we have a choice between different levels of measurement, researchers generally choose the highest level possible because it provides more information about a variable. In addition, the statistical tests we can use for interval or ratio data are more powerful than those for nominal and ordinal data, making ratio and interval scales preferred by researchers.
• Definition must be objective and precise so that others can evaluate and replicate the procedures.
• Reliability refers to the consistency of experimental operational definitions and measured operational definitions.
• Reliability means consistency and dependability. Good operational definitions are reliable:
• Interrater reliability is the degree to which observers agree in their measurement of the behavior.
• One way to assess the reliability of measurement procedures is to have different observers take measurements of the same responses; the agreement between their measurements is called interrater reliability. Typically, this method is used in content analysis, when raters must score the qualitative content of subjects' responses.
• Test-retest reliability means the degree to which a person's scores are consistent across two or more administrations of a measurement procedure.
• Reliability of measures can also be checked by comparing scores of people who have been measured twice with the same instrument. They take the test once, then they take it again (after a reasonable interval). This is called test-retest reliability.