Title EPS - MODULE 1b - Basics of Experimentation - IVs, DVs, Operational Definitions.pdf ✅

6/24/25 2 What is an experiment ? A systematic research study in which the investigator directly varies some factor (or factors), holds all other factors constant, and observes the results of the variation. The factors under the control of the experimenter are called independent variables, the factors being held constant are the extraneous variables, and the behaviours measured are called dependent variables. major differences between the two groups. Of course it is possible that there was still a participant difference but it’s much more unlikely and we don’t have any clear evidence. We could in fact test all participants using an aggression scale and hope to show that there was no significant difference between the two groups before the experiment started, without of course arousing their suspicions over the nature of the experiment. The stories for each participant are exactly the same so there can’t be any difference from these. It is of course possible that the odd story has a special effect on the odd participant which might trigger anger but we are clutching at straws if we make this kind of claim. Research methods and ethics 66 In Rule et al.’s experiment, described above, can you decide which of the following two statements makes sense and which does not? 1 The temperature in the room depended on the number of aggressive responses. 2 The number of aggressive responses depended on the temperature in the room. I hope you’ll agree that the first makes no sense in this experiment, and the second is what the experiment aimed to demonstrate. Two variables are involved in this experiment and one is traditionally known as the independent variable (IV), while the other is known as the dependent variable (DV). Could you decide now which variable (temperature in the room or number of aggressive responses) would be called the dependent variable? Pause for thought produces Manipulation of the independent variable Temperature change Change in the dependent variable Number of aggressive story endings Figure 3.2 The causal link between temperature change (IV) and aggressive response (DV). The DEPENDENT VARIABLE is the variable in the experiment whose changes depend on the manipulation of the independent variable. It is the variable we measure to see if it has changed as a result of the different conditions in the experiment. We do not know the values of the DV until after we have manipulated the IV. The INDEPENDENT VARIABLE is the variable which is manipulated by the experimenter. We know the values of the IV before we start the experiment. Here, then, the number of aggressive responses is the dependent variable and the temperature is the independent variable. The change in numbers of aggressive responses depends on the change in temperature – see Figure 3.2. The essential aim of an experiment is to demonstrate an unambiguous ‘causal link’ between these two variables. Number of bags Whether or not someone sits besides you in a train. 3 Conditions for establishing a causal inference: q Time order relationship q Co-variation q Elimination of alternative plausible causes Shaughnessy 4
6/24/25 3 BASICS OF EXPERIMENTATION § Is manipulated (viz. drug dosage) or selected (viz. sex) by a psychologist in an experiment. § Manipulated variables are under the control of E. § Factors not directly manipulated by an experimenter are referred to as ex post facto variables, natural group variables, participant variables, or subject variables (not under the control of E, assigned by nature) § Can take on any number of values, (called levels), but the minimum is two. § Can be quantitative (e.g., drug dosage) or qualitative (e.g., status – neurotic vs. non-neurotic) § Can be one or more variables manipulated/selected in an experiment § Setting: laboratory or field Goodwin and Snodgrass Can you think of how ANXIETY could be a manipulated variable as well as a selected variable? 5 BASICS OF EXPERIMENTATION Children either saw real-life aggression against a 5-foot-tall Bobo doll, a film of an adult model aggressing against Bobo. In addition, children were either male or female and the “aggressor” against the Bobo-doll was either the “same-sex” or ”opposite-sex” to the child. Children were later put in a room full of toys, including a 3-foot-tall Bobo doll, thereby giving the children the opportunity to be aggressive. The researcher assessed the aggressive behaviour of the child. The researcher was interested in whether the match/mismatch to the sex of the aggressor influenced the effectiveness of modelling on aggressive behaviour ? TIPS Naming your independent variable The IV is usually given a generic title that covers the dimension along which the levels are different values E.g. The IV of “Temperature” was manipulated at 2 levels 21o C and 31oC ACTIVITY Name the IV and it’s levels Cialdini, Reno and Kallgren (1990) the researchers arranged for 0, 1, 2, 4, 8 or 16 pieces of litter to be left on the ground to see whether this would affect whether people walking by would drop a leaflet they had just been given. 6