Overview of Exam 2 A 40 to 45 Multiple Choice Questions B Should take roughly 50 minutes to complete but you have the full 1hr15min and I ll stay longer too time is not an issue C Roughly 65 about research design concepts 35 about statistics interpreting SPSS output Stats questions will be very similar to what was asked of you in lab D Questions will be based primarily on information in the lecture slides in class lecture For studying purposes the readings are probably best used as a reference when something from your notes or the slides is unclear If a topic or term is not on the outline below it will NOT be on the exam E Topic Outline for Exam 2 Intro to Experimentation Ch 6 Lectures 10 9 10 11 1 Simple logic of Experimentation The Experimental Ideal Why it falls short with studying people Create a situation in which two groups are perfectly equal at baseline Then introduce a single treatment a single treatment a single change a single manipulation to one of the groups and take a measurement If the two groups differ on the measurement after the manipulation we can conclude that the manipulation caused this change Biggest challenges with human subjects groups are never perfectly equal at baseline and it is difficult to manipulate ONLY one thing at a time The ideal situation experiment to support a causal claim you create a situation where you can control everything possible control both groups manipulate will cause change in one Start with two groups that are the same then you do something to one group that you don t do to the other If the two groups behave differently afterward whatever you did to the experimental group must have caused the change 2 Independent Variable vs Dependent Variable IV the variable we manipulate the one that potentially causes changes in the measured variable DV the variable we measure the one that is potentially affected by the manipulation Random Assignment to Condition This reduces selection bias If you randomly assign groups to condition the probability shows that group averages tend to be normally distributed this way random selection ensures that participants in each group are similar so that way when testing a difference in a group would be from the manipulation IV and not from the participants being different or unequal at baseline Probability theory shows that if we recruit N 25 observations per group then Group averages tend to be normally distributed Groups are unlikely to be significantly different from each other just by chance alone In other words random differences wash out or average out We are unlikely replicating type 1 errors which causes group differences If we are worried that the people who actually participate are equal to those who don t participate we are worried about external validity Random assignment minimizes threat to internal validity not external validity random assignment allows us to establish cause and effect relationships Experimental vs Control Group The experimental group receives the treatment The control group or placebo group does not Experimental group receives manipulation that might affect the behavior of the individuals in that group group receives either no treatment or a standard treatment with which new Control group treatments are compared Placebo Group in medical research the comparison group in an experiment that receives what appears to be a treatment but which actually has no effect providing a comparison with an intervention that is being evaluated Randomized Double Blind Placebo control Experiment The Experimenter Effects threat is why the gold standard of experiments is that they all should contain these characteristics Randomized Double Blind Placebo control experiment Double blind a research design in which neither the investigator nor the participant is aware of the treatment being applied This means that even the experimenter does not know what condition the participant is in 3 Internal Validity Why we might have poor internal validity If we have the experimental ideal as stated above in the first bullet you have high internal validity Internal validity refers to how confidently one can conclude that the observed effect s were produced solely by the IV and not extraneous ones It is concerned with the question Was it really the treatment that caused the difference between the subjects in the control and experimental groups The IV is critical to the level of confidence you have in your conclusions the greater the internal validity the more you can have faith that you know what factors cause an individual to act in a certain way Why we might have poor internal validity o There might be random error affecting our DV Scores Aspects of the testing environment that affect both groups equally and that create noise in our data Ex a flickering light an offensive shirt worn by the experimenter the temperature of the room clutter experimenter mood ad infinitum May cause us to miss detecting an effect but is less of a problem if both groups are equally subjected to it Hard to control and especially difficult to control in Human Sciences We don t know if there is any random error so we don t ever catch it why replicating experiments is important o There might be systematic error affecting our DV scores Groups differ on a dimension that makes them unequal at baseline that is unrelated to the IV AND that may influence DV scores Ex having two conditions always run in two separate rooms or by two separate experimenters or at two times of day VERY PROBLEMATIC Must critically think how to avoid such confounds a third variable that causes that change result something other than the treatment causing the difference b w subjects a variable that is not controlled by an experimenter but that has a systematic effect on a behavior in at least one group in an experiment These errors we do have control over If we do have systematic error there is a problem if groups are different after then there is no way of knowing what it is from If they are systematically different at baseline not good need to fix this o Selection bias internal validity threat associated with participants our two groups may be predetermined by a characteristic other than our IV i e personalities of those who sit up front vs sit in back or rushing to class heart rate In other words there is an initial systematic difference before the IV Therefore they differ on two dimensions but we don t know which one caused the change Selection threat a threat to
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