Although knowledge begins with observation, the very act of observing influences the event observed. Everyday observations are likely to be uncontrolled, subjective, personalized, and impressionistic. An individual's culture provides a background of "common-sense" knowledge that tends to bias observation.
Behavioral scientists attempt to control for bias by using systematized methods such as standardized tests, scales, schedules, and tasks. They take pains to ensure that observers and measures are reliable (precise and dependable) and that measures are valid, in the sense that they measure what they mean to measure.
To be truly scientific, an investigation must follow a basic set of rules: it must be replicable, and it is likely to begin with a hypothesis about the relationship of several variables; the variable that is hypothesized as causal is the independent variable, and the variable that it influences is the dependent variable.
The experimental method is the classic form for S-R research. A stimulus (the independent variable) is systematically introduced in a controlled situation, and the experimenter observes the subject's response (the dependent variable). The experimenter must, however, take steps to ensure that the observed effect is caused by the independent variable, and not by other variables that may appear in association with it. In determining the effect the voice of an infant's mother has on his behavior, for example, the researcher must be sure that the infant is reacting to his mother's voice and not to adult female voices in general. Hence the researcher institutes a control by exposing the infant not only to his mother's voice but to the voice of a strange adult female as well. Age and sex are variables that are usually controlled, and reliability is insured by employing more than one judge or rater of the dependent variable. The experimental group's performance may also be contrasted with that of a comparable control group.
S-R or experimental research is one kind of technique in behavioral study. Another is R-R research, or correlational/differential methods, in Which responses are compared or contrasted. This technique is often employed in studies of cross-cultural differences and child-rearing practices, as well as in other types of investigations that do not lend themselves to experimental manipulations of the S-R type. In such studies, pre-existing conditions, attitudes, and values are usually considered to be independent variables, with performance in test situations the dependent variable. Often S-R and R-R methods are used in combination.
Correlation is the statistic most widely used in developmental psychology. Most correlational studies employ the Pearsonian coeffi-