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CHAPTER 2: The Scientific Method 37FIGURE 2.3Scientific instruments used in psychology have improved dramatically in their precisionand accuracy.improved significantly since 1879, the founding of the first psychology laboratory.Today, many sophisticated instruments are used in contemporary psychology(Figure 2.3). To perform a psychophysiology experiment (e.g., whenassessing a person’s arousal level) requires instruments that give accurate measuresof such internal states as heart rate and blood pressure. Tests of anxietysometimes employ instruments to measure galvanic skin response (GSR). Otherbehavioral instruments are of the paper-and-pencil variety. Questionnaires andtests are popular instruments used by psychologists to measure behavior. So, too,are the rating scales used by human observers. For instance, rating aggression inchildren on a 7-point scale ranging from not at all aggressive (1) to very aggressive(7) can yield relatively accurate (although perhaps not precise) measures ofaggression. It is the responsibility of the behavioral scientist to use instrumentsthat are as accurate and as precise as possible.MeasurementScientists use two types of measurements to record the careful and controlledobservations that characterize the scientific method. One type of scientificmeasurement, physical measurement, involves dimensions for which there is anagreed-upon standard and an instrument for doing the measuring. For example,length is a dimension that can be scaled with physical measurement, andthere are agreed-upon standards for units of length (e.g., inches, meters). Similarly,units of weight and time represent physical measurement.In most psychological research, however, the measurements do not involvephysical dimensions. Rulers do not exist for measuring psychological constructssuch as beauty, aggression, or intelligence. These dimensions require asecond type of measurement— psychological measurement. In a sense, the human