Experimental Methods:
One very common research method is to manipulate [manipulation the process of systematically varying an independent variable across different experimental conditions (sometimes referred to as the experimental treatment or intervention)] one or more variables and to examine the effect of this manipulation on an outcome variable. To do this, the researcher examines participants’ responses in the presence and the absence of the manipulation. Experimental control is used to make the different situations identical in every respect except for the presence or absence of the manipulation. Experiments can involve different people in each situation or the same people in different situations [experimental control the method of ensuring that the groups being studied are the same except for the manipulation or treatment under investigation]. People who take part in experiments are called participants, but if you read older research papers they are generally referred to as subjects. Here is an example. To test the effect of a new training method (a manipulation) on memory, we might take 100 people and expose half of them to the new method. For reasons we will discuss in more detail below, we would assign participants to the two groups on a random basis (e.g. by the toss of a coin). We will call the first group the experimental group, as it is subjected to a relevant experimental treatment [experimental group participants in an experiment who are exposed to a particular level of a relevant manipulation or treatment (as distinct from a control group)] . The other half of our participants would not be exposed to the new training method. As they receive no experimental treatment, [treatment the experimental manipulation of the independent variable] they are referred to as a control group (also discussed in more detail below) [control group participants in an experiment who are not subjected to the treatment of interest (as distinct from the experimental group)] . After administering the treatment, we would measure the performance of the two groups on a memory task and then compare the results. The various levels of treatment in an experiment (including the control) are referred to as conditions. [condition a situation in a research study in which participants are all treated the same way]
This experiment has two conditions and a between-subjects design (because the design involves making comparisons between different participants in different conditions). [between-subjects design a research study involving a systematic manipulation of an independent variable with different participants being exposed to different levels of that variable] Note, however, that the same question could also have been addressed in a withinsubjects design, [within-subjects design a research design in which the same participants are exposed to different levels of the independent variable] which would involve comparing the memory performance of the same people with and without the new training method. The two basic designs have different strengths and weaknesses, which we will discuss below in relation to issues of experimental control. The different conditions in the experiment make up the independent variable (or IV), [independent variable the treatment variable manipulated in an experiment, or the causal variable believed to be responsible for particular effects or outcomes] sometimes called the treatment variable. A variable is simply something that changes or varies (is not constant). In true experiments, the independent variable is systematically manipulated or varied by the experimenter.
Experiments can (and typically do) have more than one independent variable. Experiments also involve at least one dependent variable (or DV).[ dependent variable the variable in which a researcher is interested in monitoring effects or outcomes] This is an outcome or measurement variable, and it is this variable that the experimenters are interested in observing and which provides them with data. In our last example, the dependent variable is the level of memory performance. Use the initial letter ‘d’ to remember the link between the dependent variable and the data it provides. Control is the basis of experimental design. It involves making different conditions identical in every respect except the treatment (i.e. the independent variable). In a between-subjects experiment, this is achieved by a process of random assignment of participants to the different conditions[random assignment the process of assigning participants to study conditions on a strictly unsystematic basis]. For example, people should be assigned at random (e.g. on the basis of coin tossing),rather than putting, say, the first 50 people in one condition and the second 50 in another. This practice rules out the possibility that there are systematic differences in, say, intelligence, personality or age between the groups.
If there is a difference in results obtained from measuring the dependent variable for each group, and we have equated the groups in every respect by means of random assignment, we can infer that the difference must be due to our manipulation of the independent variable.
One very common research method is to manipulate [manipulation the process of systematically varying an independent variable across different experimental conditions (sometimes referred to as the experimental treatment or intervention)] one or more variables and to examine the effect of this manipulation on an outcome variable. To do this, the researcher examines participants’ responses in the presence and the absence of the manipulation. Experimental control is used to make the different situations identical in every respect except for the presence or absence of the manipulation. Experiments can involve different people in each situation or the same people in different situations [experimental control the method of ensuring that the groups being studied are the same except for the manipulation or treatment under investigation]. People who take part in experiments are called participants, but if you read older research papers they are generally referred to as subjects. Here is an example. To test the effect of a new training method (a manipulation) on memory, we might take 100 people and expose half of them to the new method. For reasons we will discuss in more detail below, we would assign participants to the two groups on a random basis (e.g. by the toss of a coin). We will call the first group the experimental group, as it is subjected to a relevant experimental treatment [experimental group participants in an experiment who are exposed to a particular level of a relevant manipulation or treatment (as distinct from a control group)] . The other half of our participants would not be exposed to the new training method. As they receive no experimental treatment, [treatment the experimental manipulation of the independent variable] they are referred to as a control group (also discussed in more detail below) [control group participants in an experiment who are not subjected to the treatment of interest (as distinct from the experimental group)] . After administering the treatment, we would measure the performance of the two groups on a memory task and then compare the results. The various levels of treatment in an experiment (including the control) are referred to as conditions. [condition a situation in a research study in which participants are all treated the same way]
This experiment has two conditions and a between-subjects design (because the design involves making comparisons between different participants in different conditions). [between-subjects design a research study involving a systematic manipulation of an independent variable with different participants being exposed to different levels of that variable] Note, however, that the same question could also have been addressed in a withinsubjects design, [within-subjects design a research design in which the same participants are exposed to different levels of the independent variable] which would involve comparing the memory performance of the same people with and without the new training method. The two basic designs have different strengths and weaknesses, which we will discuss below in relation to issues of experimental control. The different conditions in the experiment make up the independent variable (or IV), [independent variable the treatment variable manipulated in an experiment, or the causal variable believed to be responsible for particular effects or outcomes] sometimes called the treatment variable. A variable is simply something that changes or varies (is not constant). In true experiments, the independent variable is systematically manipulated or varied by the experimenter.
Experiments can (and typically do) have more than one independent variable. Experiments also involve at least one dependent variable (or DV).[ dependent variable the variable in which a researcher is interested in monitoring effects or outcomes] This is an outcome or measurement variable, and it is this variable that the experimenters are interested in observing and which provides them with data. In our last example, the dependent variable is the level of memory performance. Use the initial letter ‘d’ to remember the link between the dependent variable and the data it provides. Control is the basis of experimental design. It involves making different conditions identical in every respect except the treatment (i.e. the independent variable). In a between-subjects experiment, this is achieved by a process of random assignment of participants to the different conditions[random assignment the process of assigning participants to study conditions on a strictly unsystematic basis]. For example, people should be assigned at random (e.g. on the basis of coin tossing),rather than putting, say, the first 50 people in one condition and the second 50 in another. This practice rules out the possibility that there are systematic differences in, say, intelligence, personality or age between the groups.
If there is a difference in results obtained from measuring the dependent variable for each group, and we have equated the groups in every respect by means of random assignment, we can infer that the difference must be due to our manipulation of the independent variable.
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