Research Methods example 2 I want to test the effect of Hours spent Studying on Exam Performance. VARIABLES The Independent Variable is Hours spent Studying (this is what I want to see the effect of, what I am going to vary or manipulate, I am going to get people to either study or not study and then take an exam) The Dependent Variable is Exam Performance (this is what I am going to measure to see any effect the IV has had, I am going to record their performance on the exam) FINDING A SAMPLE OF PARTICIPANTS My Population of interest is all year 12 students in Victoria. Obviously I cannot test every year 12 student in Victoria so I will draw a smaller sample of students to represent the larger population. Before I draw my sample I need to consider if there are any groups within my population of interest that may test differently to other groups. If there are I need to make sure that these groups are represented in my sample, if they are not then my sample is not representative and my results will be meaningless. For example the type of school attended by the students (public or private) in my study may affect their exam performance. Thus I need to make sure that I use stratified sampling. I must divide the population into groups based on the type of school attended, (eg. Public or private) and then draw my sample randomly from within each of these groups. Doing this will ensure that my sample contains the same proportions of males and females as appear in the population. Eg. If in the population 50% of students attend public schools and 50% attend private schools and I am drawing a sample of 100. To stratify my sample and make it truly representative of the population I must randomly draw 50 public students and 50 private students from the population. EXPERIMENTAL AND CONTROL GROUPS To test whether studying effects exam performance I need to organize my experiment. I need to divide my participants into two groups. One group will study and then complete the exam; the other group will not study and then complete the same exam. Doing this allows me to compare the performance on the exam of people who studied Vs people who did not study. Group One is the Experimental group – they were exposed to the IV (studying) Group Two is called the Control group – they were not exposed to the IV (they did not study) Now I can compare the difference in performance between the experimental and control groups and find out if studying affected exam performance. Wrong answer dumb arse!!! If you study you will do well you stupid little boy!!! EXTRANEOUS VARIABLES Once I have obtained my sample of students I must consider other factors before I assign participants to the experimental and control groups. There are lots of things which are specific to the individuals I have chosen for my study that may affect exam performance other than studying. These factors are called extraneous (uncontrolled) variables These might include: intelligence, anxiety, previous experience etc. If I simply use random allocation to decide who will be in the Experimental and Control groups I may get a severe mismatch that will affect my results. For example my experimental group may have all of the students who are intelligent and my control group may have all of the students who are not intelligent! Eg. If by chance my experimental group contains all of the students in my sample who are intelligent then I cannot know if my experimental group performed better on the exam because they studied or because they were just smarter than the control group! Now my results are meaningless! I don’t know if it was studying or intelligence that effected exam performance. If this happens the extraneous variable has become what we call a confounding variable. We don’t know which variable has had an effect, our IV or the extraneous (now referred to as confounding) variable. Was it studying? OR Intelligence? that caused our experimental group to perform better? CONTROLING EXTRANEOUS VARIABLES To control extraneous variables we need to make our experimental and control groups as similar as possible. If they are identical in almost every way then any difference between them should be due to the effects of the IV not other factors. Eg. If we make sure that there is the same number of intelligent and stupid individuals in the experimental and control groups then intelligence should not create a difference in exam performance between our groups. Any difference in exam performance should be due to the effects of studying. There are a number of ways we can ensure our experimental and control groups are as similar as possible on all factors except the IV Repeated Measures Design (Stroop used this) Each participant is involved in both the experimental and control conditions. This design controls or eliminates any effects that might be attributed to participant's personal characteristics, since they remain constant. Also known as the within participants design. Little Jimmy will first complete the Little Jimmy will then complete an exam without studying equivalent exam after studying CONTROL GROUP EXPERIMENTAL GROUP Note that an equivalent exam is used in the second condition. Why am I in your study again Mr Brinkman??? Quiet Jimmy!!!!! The only problem with this is that participants’ performance on the second condition may be affected by their past experience of having done an exam before. This is called Order Effect. Counterbalancing is used to control this. Counterbalancing involves making half of the participants do the two conditions in one order (control then experiment) and the other half in the opposite order (experiment then control) Matched Participants Design – Paired up Involves selecting pairs of participants who are similar in characteristics that can influence the dependent variable, on the basis of scores achieved on a pre-test, or a number of pre-tests. Participants are then ranked and paired in accordance with their scores and then one of each pair is allocated to the experimental and the other to the control group. Doing this ensures the experimental and control groups are as similar as possible on all other factors other than the presence of the Independent Variable All participants are given an intelligence test prior to our study beginning. The two participants with the worst IQ are paired up. One of the pair is then assigned to the experimental group the other to the control group. Eg. Fred and Johnny were the two participants who scored lowest on the IQ test Fred scored equally as bad as Johnny on the IQ test. Fred is now assigned to the CONTROL GROUP Johnny scored equally as bad as Fred on the IQ test. Johnny is now assigned to the EXPERIMENTAL GROUP I may look cool but I’m really stupid! Duh! Independent Groups Design Allocates participants to groups via a random procedure such as the toss of a coin. Then all those who toss a head might be allocated to the control group and all those who toss a tail to the experimental group. This only works when our experimental and control groups are very large. The idea being that if we have enough people then most of the extraneous variables will cancel themselves out just by chance! Boris tossed a head so he goes into the CONTROL GROUP Some dude in a suit of armour tossed a tail so he goes into the EXPERIMENTAL GROUP