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PSYCO 105 (09/12/13) Methods (con't) & Psychological Disorders

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Eric Legge

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PSYCHO 105 (September 12, 2013) Topic 1: Methods (con’t) & Topic 2: Psychological Disorders  Experimentation is the only way to find causal relationship o Must be conducted in a controlled environment  Main thing is to manipulate such variables in this setting and see what effects arise from it. Manipulation – the act of created artificial variation; in experimentation, it is for the sole purpose of finding causal relationships There are 4 Critical Steps in Manipulations Step 0: (this step is not included in the textbook but is critical!)  Make sure you know your independent and dependant variables as well as what and in what units you will be measuring in  Decide on a design: o Between subjects design: One control group and one ‘treatment’ group o Within-subjects design: The participants act as both the control group AND the ‘treatment’ group (ex. Before and after experiments)  Problems: Residual effects? Long-term effects? Interference? Step 1: Manipulation of the IV (Independent Variable)  Example: Give a drug to one group (‘treatment’ group) and a placebo to the other group (control group) Placebo: harmless substance/solid that appears like the treatment drug used in the study (ex. Sugar pill, saline injection) Step 2: Measure DV (dependant variable) if applicable  Example: Give participants of both groups a mood survey Step 3: Check to see if ‘treatment’ group has been affected differently from the control and draw conclusions  Example: Was there a difference in mood between the two groups? Random Assignment Random assignment: randomly choosing people and then assigning them to predetermined groups at random Sample: a portion of a population chosen to participate in a study Population: the entire group from which you want to draw a general conclusion from choosing a sampling  Non-Random assignment: o Ex. People who want to participate in a study sign themselves up on a signup sheet and the top half are assigned to be a part of the control group while the other half is assigned to be a part of the ‘treatment’ group  Problems:  What if there were significant differences between the two halves of the people concerning the data you wanted to measure  Participant group may be biased because you are only getting a sample of people WILLING to participate in the experiment and not the other people who contribute just as much to the overall population  Ideally, through random assignment, you results should reflect and support that of the general population  Random assignment is an important tool BUT we cannot draw firm conclusion about the arising results o Example: coin-flipping probability is 50/50 BUT it is very unlikely that actually flipping them will yield 50 heads and 50 tails unless you were to flip an infinite amount of times. In the sampling of infinite flips, you can get ratios like 70/30 and 60/40 Significance  The results from experiments psychologists carry out are only ‘meaningful’ IF they are 95% sure that their random assignment has not “failed” o p < 0.05 (p = probability that random assignment has failed) o Such experiment results lead us to say that this experiment has internal validity Internal validity – experimental characteristic that is able to establish a causal relationship between the IV and the DV  Even though an experiment has internal validity, it only means that the relationships are true for the particular group of people from which we sampled from o In order to draw broad conclusion about a whole population, an experiment must have external validity  The variables must have operationally defined variables in a normal, typical, or realistic way.  Example: Research participation for university students does not yield results that help people draw a broad conclusion about the world’s population as a whole. (No external validity) University students have characteristics that may not be universal (ex. Education, level of wealth, stress, differing cultural influences)  In order to get results which reflect the general population closely as possible, you will have to do some random sampling Random sampling – method for selecting participants such that every member in a population has an equal chance of being represented in the created sample group  Perfect random sampling is a rare occurrence though: o Not much of a problem to psychologists though o Theories and experiments designed in a way that allows inability to randomly sample  We are just looking for the existence of a certain result and NOT the general results for the whole population o Failure to randomly sample is not a big deal because:  Sometimes there is no need for the sample group and the population to be similar  Experiments can be conducted many times using a different sample group. Resulting similarities or dissimilarities can be used to generalize or disprove findings respectively  Sample and population traits are usually reasonably similar as is (ex. Brain size in people of different countries)  Worst case of representative populations = case studies o Why? Because they only involve 1 individual  Results cannot be used to represent a whole population because of this o Case studies are good for some things though:
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