In scientific research, a hypothesis is a statement about  a  predicted  relationship  between  variables. A good research hypothesis can be formulated as an “if-then” statement:

  • If a child is exposed to the music of Mozart, then that child’s intelligence will increase.
  • If students learn a math lesson by interacting with a computer, then they will solve math problems more accurately than students who learn the same lesson by listening to a lecture.

Notice that a hypothesis is not a question. It is a statement,  a  prediction  that  requires  the  researcher to go out on a limb and say what he or she thinks will happen in a given situation. When stating a hypothesis, the researcher must run the risk of being wrong—a scientific hypothesis must be falsifiable.

Hypotheses come from many sources. Researchers are not all wildly creative people, but they do tend to be careful observers of the world around them. One’s own everyday observations can lead to the formulation of a hypothesis, as when a babysitter observes that “children who eat ice cream before bedtime have a harder time falling asleep.” That simple observation can lead to a formal hypothesis about the relationship between sugar consumption and sleep onset. A famous hypothesis in social psychology was generated from a news story, when a woman in New York City was murdered in full view of dozens of onlookers. Instead of simply shaking their heads in sadness, psychologists John Darley and Bibb Latané developed a hypothesis about the relationship between helping behavior and the number of bystanders present, and that hypothesis was  subsequently  supported  by  research.  This  type of reasoning from a specific case to a more general principle is called inductive logic.

Reading existing research and theory can also lead to the generation of hypotheses. Through the process of deductive logic, a general theory leads to the prediction of a specific effect or conclusion. For example, someone who is familiar with Piaget’s theories of human development might predict that “if a child is younger than the age of 12, then that child will be unable to solve an abstract reasoning problem.” Such a hypothesis could then be put to the test in systematic research.

Hypotheses can be either directional or nondirectional. A directional hypothesis states a specific prediction about the precise type of effect that a variable is expected to have on another variable—for example, “If the number of bystanders increases, then the probability of any given bystander rendering help decreases.” A nondirectional hypothesis states that a relationship will exist between two variables, but it is not specific about the nature of that relationship: “If the number of bystanders increases, then the probability of any given bystander rendering help will change.” This type of hypothesis can be confirmed if the probability of help increases or if it decreases. Nondirectional hypotheses are useful in the early stages of research in a given area, when the researcher may not have enough information  to  make  a  more  specific  prediction. A nondirectional hypothesis is still falsifiable, however, if the data suggest that there is no systematic relationship between the variables after all.

Whether directional or nondirectional, a good research hypothesis must ultimately be objectively testable. Before actually turning a hypothesis into a study, the researcher must develop operational definitions of the variables stated in the hypothesis. If the hypothesis postulates that “If a child is exposed to the music of Mozart, then that child’s intelligence will increase,” then the researcher must define what specifically is meant by “child” (a person under the age of ?), by “intelligence” (a score on a particular standardized test, perhaps), and what it means to be “exposed” to the music of Mozart (Which compositions by Mozart? For how long? Played how loudly?). Thus, the development of the hypothesis is only the beginning of the process of psychological research.


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