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In attempting to answer questions about human behavior scientifically, researchers must use scientific methods. These methods are designed to help scientists describe, predict, and explain behavior. Descriptions are best obtained through carefully measured firsthand observation. In making predictions, scientists use past behavior as a reliable predictor of future behavior (Theme 1). The different theoretical orientations, discussed in Chapter 1, play an important role in how psychologists explain behavior. Finally, although changing behavior is not one of the essential goals of psychology, it is an important practical application.
To study human behavior, scientists must select a target group or sample. A sample should adequately and fairly represent its population. This can be accomplished in two ways. In random sampling, each member of a population has an equal chance of being selected in the sample. In representative sampling, a chosen group exactly matches the population on some characteristic(s) such as sex or age, in terms of the percentages in the sample and in the population overall. Samples, even when they are very large, can misrepresent a population if they are drawn from a subgroup of the population.
Psychologists can describe their samples in a number of ways, including case studies, naturalistic observations, and surveys. A case studyis an intensive investigation of one person, rather than a representative group, usually because the observed behavior is rare or unique. Thus, psychologists learn about the normal by studying the abnormal (Theme 2). Naturalistic observation involves watching and recording behavior as it naturally occurs. There are two major limitations to this method. First, there is a tendency to behave differently among people who believe they are being observed. Second, because of the lack of experimental controls, causality cannot be inferred. A survey is an attempt to estimate the opinions, characteristics, or behaviors of a particular population.
One way researchers analyze their data is by using a correlational design, which allows them to find relationships between variables. One type of correlational technique, regression, uses the relationship between variables to make predictions. A positive correlation means that as one variable increases, so does the other. A negative correlation means that as one variable increases, the other decreases. Correlations can be represented numerically by a correlation coefficient. Correlation coefficients express the degree of relationship between two variables. They range from -1 (a perfect negative correlation) to a +1 (a perfect positive correlation). A 0 correlation indicates no relationship between the variables; the closer a correlation coefficient approaches either -1 or +1, the stronger the relationship between the two variables.
In an experimental design, participants are randomly assigned to conditions. Random assignment is used to help compensate for the researcher’s inability to control for all the participants’ characteristics. It is assumed that any characteristic will be equally represented in both groups. The experimental group consists of those participants who experience the experimental condition. The control group consists of participants who will experience all that the experimental group does except for one variable or factor capable of change. The control group is needed so that comparisons can be made. Differences between these two groups are assumed to be a causal result of the manipulation of the independent variable by the experimenter. Again, this variable affects the dependent variable, which is the variable the experimenter measures.
Experiments can be used to better understand the influence of the environment on human behavior. However, both heredity and the environment are important determinants of behavior. Heredity refers to an inherited set of developmental instructions that are transmitted through genes, chemical "recipes" for building an organism. Chromosomes are the structures that store material to be passed on from one generation to the next. The environment refers to all the other influences we encounter.
Behavioral geneticists have studied twins and adopted children to better understand the separate influences of genetics and the environment. Monozygotic (identical) twins share 100% of their genetic material. Dizygotic (fraternal) twins share 50% of their genetic material. Adopted children generally share no genetic material with other children in their families. By comparing groups of siblings who have shared environmental influences, but differ in their levels of genetic similarity, behavioral geneticists can draw inferences about the extent of the influence of genetic and environmental factors.
Behavioral geneticists argue that heritability (h2) and environmental factors (e2) determine an individual’s behavior. Environmental factors are divided into shared environmental influences (ES) and nonshared environmental influences (ENS). Determining the role of each of these components is essentially the work of behavioral geneticists.
Statistics are mathematical methods used for assessing and presenting data in summary form. Descriptive statistics are a form of shorthand for representing a large amount of data. For example, measures of central tendency measure the most characteristic score for a group. Three measures of central tendency are commonly used: the mean (or arithmetic average of the scores), the median (or middle score), and the mode (or most frequent score).
In addition to knowing central tendency, psychologists also need to know how scattered scores are, a characteristic called dispersion, or variability, of the scores. The range is one measure of variability, and it is simply the difference between the highest and lowest scores. The standard deviation is generally the more preferred measure because it indicates the average extent to which all scores in a particular distribution vary from the mean.
When a distribution of data is symmetrical, the mean, median, and mode are identical. Such a symmetrical distribution is called a normal distribution, or normal curve.
Many problems can invalidate a study. The self-fulfilling prophecy is the notion that expectations of investigators can influence findings. One method used to alleviate this problem is the double-blind technique, in which neither the experimenter nor the participants knows who is in the experimental and control groups. In a variation, the single-blind technique, the experimenter knows who is in which group, but the participants do not.
Demand characteristics are conditions that cause participants to respond in ways they think will please the experimenter. Demand characteristics can change behavior even if a participant is not consciously aware of them. This can be taken as further evidence that a large proportion of behavior is controlled by unconscious activity (Theme 3). Demand characteristics can be reduced by avoiding face-to-face encounters with participants and by interviewing participants after the experiment to detect any demand response patterns. Demand characteristics can also be reduced by deceiving the participants about the real intent of the experiment. In this case, participants must be debriefed afterward and informed of the experiment’s real purpose.
The Hawthorne effect is the phenomenon of participants’ awareness of participating in an experiment affecting their performance. Replication--that is, repeating an experiment--serves as an essential check, making sure that the results of the experiment are reliable and dependable. Multiple studies help to avoid premature conclusions.
The American Psychological Association (APA) has issued ethical guidelines for studies involving human participants. According to these guidelines, research should not cause lasting physical or psychological harm. Participants’ involvement must always be voluntary, and if they request, participants should be allowed to withdraw at any time during an experiment. If deception is used, the experimenter must later explain why it was necessary. Finally, participants’ privacy must be protected.
Other organizations also insist on ethical treatment; these include the U.S. government and most universities. Also, public and private institutions protect the rights of animals in experiments. In recent years, very few complaints have been made against psychologists regarding the treatment of human and animal participants.
In the late 1970s, cognitive psychologist Ulric Neisser made a provocative statement criticizing research for its lack of ecological validity, or relevance to the "real world." A debate ensued over which was more important, ecological validity or scientific integrity. Those emphasizing the importance of scientific integrity favored experimental designs. Those emphasizing ecological validity favored naturalistic designs. Today, trade-offs between ecological validity and scientific control continue to be important considerations for researchers.
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