The experimental method is one of the most systematic and scientific methods used in psychology to study human and animal behaviour. Psychology deals with observable behaviour as well as internal mental processes, and the experimental method helps researchers understand the relationship between different psychological variables under controlled conditions. It involves deliberate manipulation of one variable, observation of its effects on another variable, and control of other factors that may influence the outcome. Because of its emphasis on objectivity, measurement, control, and replication, the experimental method occupies an important position in behavioural sciences. An experiment generally begins with the identification of a psychological problem or research question. The researcher clearly defines what is to be studied and develops a hypothesis. A hypothesis is a tentative statement about the expected relationship between variables. For example, a psychologist may hypothesize that lack of sleep reduces attention and concentration. The hypothesis provides direction to the experiment and enables the researcher to determine what information needs to be collected. The next important step is the identification of variables. A variable is any characteristic or condition that can change or take different values. In an experiment, the independent variable is the factor that the researcher deliberately manipulates. The dependent variable is the behaviour or psychological outcome that is measured to determine the effect of the independent variable. For example, if the researcher studies the effect of sleep deprivation on concentration, the amount of sleep may be treated as the independent variable, while performance on an attention test may be the dependent variable. Other factors that could influence the result are treated as extraneous variables and are controlled as far as possible. Control is a central feature of the experimental method. The researcher attempts to ensure that changes in the dependent