Child psychologists use thescientific method in their research. They formulate hypotheses on the basis of theories, and they use measurable and replicable techniques to collect, study, and analyze data to test the usefulness of these theories. SELECTING A SAMPLE Selecting a sample is an important first step in doing research because it will determine the extent to which the researcher's conclusions can be applied, or generalized, to people other than those who were studied.Some Solutions to the Problem of Representativeness To ensure therepresentativeness of a sample, or the degree to which it accurately reflects the larger national population, it must include individuals who vary by such factors as race, sex, and social class.Another Approach: The National Survey Conducting anational survey is another way to ensure that a sample is representative of a broad range of people. METHODS OF GATHERING DATA ABOUT CHILDRENChildren's Self-Reports Soliciting self-reports from children, usually by means of interviews, is one way to gather information about child development issues. Getting self-reports from children can be more difficult than getting them from adults for children tend to be less attentive, slower to respond, and less likely to understand the questions put to them. Self-reports, however, are the only way to obtain information about such things as children's feelings and their unique perspectives on their lives.Reports by Family Members, Teachers, and Peers Another data-gathering method is to solicit information about a child from other people who know that child well, such as parents, siblings, teachers, and peers. Attempts that increase the accuracy of parents' reports about their children include focusing on specific current issues in the child's life, training the parents to be more accurate observers, using structured diaries to guide their observations, and "beeping" them at various times to tell them when to record information.Direct Observation Often, of course, there is no substitute for researchers' owndirect observation of children. Such observations can occur in natural settings, such as a child's home, or in a laboratory; in the latter case, astructured observation allows researchers to observe the child as he performs some highly structured task. One limitation of direct observation is that when children and parents know they are being watched, they tend to act in more socially acceptable ways than the ways in which they ordinarily behave. To minimize such distortions, researchers try to observe unobtrusively for relatively long periods of time to enable subjects to adapt to the situation. When researchers use direct observations, they must decide what kinds of behaviors to record. They can write down everything the participant does (a specimen record), record only particular events (event sampling), or check off a list of behaviors that occur in a predetermined period of time (time sampling). If the researcher wishes to examine the stream of behavior, a better strategy is to record events in sequence. If the research question involves infrequently occurring behaviors, the researcher can structure the situation to increase the likelihood that the behavior will take place. Because of the limitations of all data-gathering methods, researchers often use multiple measures of the same behaviors. RESEARCH DESIGN: ESTABLISHING RELATIONSHIPS AND CAUSESThe Correlational Method Thecorrelational method involves examining the relationship between two events, such as preschool children's aggressiveness and the amount of aggression they watch on television. Thecorrelation coefficient is expressed in terms of the direction (positive or negative) and size (-1.0 to +1.0) of the relationship. If two factors are correlated, they are systematically related to each other, but a correlation alone does not tell us whether one factor caused the other.The Laboratory Experiment Alaboratory experiment permits researchers to establish cause-and-effect relationships by assessing a specific behavior (such as trying to hurt another person) in a controlled laboratory setting where a certain factor of interest (such as viewing TV violence) is introduced to anexperimental group of participants while acontrol group is exposed to some neutral factor. Researchers use arandom assignment to assign participants to either of these groups. The dependent variable is the behavior that is affected by the manipulation of the independent variable. The problem with laboratory experiments is that they rarely haveecological validity and cannot easily be generalized to real-world settings. In alaboratory analog experiment a researcher duplicates in a laboratory many of the features of a natural setting. This approach allows control over the situation while preserving some of the "naturalism" of real situations.Field and Natural Approaches Even less artificial is afield experiment, in which a researcher deliberately produces a change in a real-life setting and measures the outcome there. Nevertheless, researchers have to guard againstobserver bias when working in the field. Another alternative to increase the generalizability of the findings is to conduct anatural experiment. In this case, the investigator measures the impact of a naturally occurring change on the child's behavior in a real setting. But because of lack of control over the independent variable and other factors that could affect behavior, it is often difficult to interpret the results of a natural experiment.Combination Designs in Developmental Research The various types of experiments available to researchers illustrate an important trade-off between experimental control and the generalizability of findings. No single strategy is always best. Rather, investigators are increasingly using multiple research strategies to study relationships and causes.The Case Study Approach Thecase study method takes an in-depth look at a single child, often (but not always) one with some rare disorder, an unusual ability, or some other uncommon feature that makes him or her of special interest to developmentalists. One form of the case study is theABAB design, in which researchers first measure a child's baseline behavior, and then introduce, withdraw, and reintroduce the independent variable to discover its effects on behavior. STUDYING CHANGE OVER TIMEThe Cross-Sectional Method The most common strategy for investigating developmental change over time is thecross-sectional method, in which researchers compare groups of children of different ages at a given point in time. This approach is economical in both time and money, but it yields no information about change nor does it yield information about the causes of any observed age-related differences in the child participants.The Longitudinal Method Thelongitudinal method overcomes these two drawbacks of cross-sectional research because the researcher examines the same children at different points in their lives. But longitudinal research has its own disadvantages, including high cost, gradual loss of subjects, limited flexibility in using new insights or methods once the study has begun, and the applicability of the findings to otherage cohorts.The Sequential Method To overcome some of these limitations, researchers can use thesequential method, which combines features of both cross-sectional and longitudinal studies. This design enables researchers to compare not only groups of different ages at one point in time, and to track individual children over a period of years, but also to track age cohorts over a number of years. THE ETHICS OF RESEARCH WITH CHILDREN A major consideration when deciding on a research strategy is the effects of the procedures on participants. Various government and institutional review boards, in addition to professional organizations, are involved in setting and maintaining guidelines for the proper treatment of human subjects in research. These guidelines include the right to be fully informed about the nature of a study and its procedures, the right to giveinformed consent before participating, and the right not to be harmed. But as easy as it is to list such rights of human subjects, it is not always easy to determine the ethical course of action in a particular situation. To determine if certain research procedures are ethical or not, the costs to participants must be carefully weighed against the potential benefits of increased knowledge about development.