EESA05 - Environmental Hazards - Lec 6 - near verbatim

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Environmental Science
Mandy Meriano

PSYB01 Lecture 6: PY Date: Experiments Still in the testing phase Demonstration: Taste test comparing diet pepsi in bottle and diet coke in Heros cup Should have been at the same temperature; there were more than one variable One was in the bottle itself and the other was in the generic cup There was also personal opinion and he knew which was which; should have covered up both so he didnt know which was which Prof tried to persuade him to choose one over the other This was NOT a good experiment There were so many variables that couldve influenced his decision Previous lecture relationship btn variables correlations Calculate and make scatter plot see how variables are related Strong positive correlation Perfect positive correlation Weak correlation Not related to each other Ex) kids eat good breakfast academic performance better relationship o Question: is eating breakfast CAUSE better performance? o Probably not. Its probably if you eat breakfast, youre better able to pay attention b/c youre not hungry, stomach not grumbled, not distracted. So breakfast doesnt CAUSE better performance. Something else at play. Ex) teen females having eating disorders related to them watching soaps Key point: correlational results can only tell you so much; can only say that 2 variables are related to each other, cant say in what way theyre related o Does one cause the other, or is there a third variable at play? In order to answer causal questions, need to conduct an experiment. Cant assume that just because 2 things are correlated, that its causal there could be other things that are happening. Problems with establishing causality in correlational research Direction of influence problem o Could be in the opposite direction of what you think o Ex) class attendance and grades strong relationship; most ppl think that if you go to class, then you get higher grades; that may not be the case could be that ppl who get good grades are more likely to go to class o Direction of causality which causes which? Third variable problem o Third variable that causes the changes in both of the variables that you correlated o Ex) positive mood and charitable donations are positively correlated may be that theres 3 variable involved thats causing both of those things maybe just got paid, which makes them in good mood and more likely to make charitable donations at that time 1 PSYB01 Lecture 6: PY Date: o Ex) correlation btn ice cream sales and drowning; third variable temperature when temp = high, ice creams sales are up, more ppl go swimming and more drowning Sometimes may have both direction of influence problem and third variable problem o Correlation btn depression and sleep disturbances could be that depression is causing the disturbed sleep, could be that the disturbed sleep is making the person depressed or that theres 3 variable (ex: family problems causing depressed mood and loss of sleep) Three things needed to establish causality (must use experiments and they must include the following): Temporal order must be correct o Cause has to come before the outcome o With correlational research (unless you have some kind of longitudinal component where you can tell what happened first) you cant establish this Variables have to covary o As in correlation, they have to vary together No other variable is causing the outcome Experiments are the way that you can get these 3 things to happen Extraneous vs confounding variable Must hold all extraneous variables constant like container that drink was in, the temp of drink, the way it was presented to taste testers o May still have some influence but itll be the same influence for all the diff participants Extraneous variables = anything other than the independent variable that could have an effect on the DV Confounding variables are related to the independent variable they vary along with the independent variable so its hard to tease out the separate effects o The drinks the temperature of the drink was confounded with the type of drink Dont know if its drink itself or the temp of drink thats causing ppl to prefer one over the other o Confounding variables = subset of extraneous variables *all confounding variables are extraneous variables but not all extraneous variables are confounding variables How experiments allow you to do this: Hold all variables constant Use random assignment o If theres anything that you cant hold constant or control then use random assignment on random basis, assign ppl to one condition or another (ex: random #s table) 2 diff conditions that ppl need to be in; 1 and 2 put in hat and draw it out will decide if person in group one or 2 Present i.v. first 2PSYB01 Lecture 6: PY Date: o IV is the causal factor and therefore is presented first this takes care of the causal factor Present i.v. carefully and consistently, measure the d.v. rigorously o Operationalize DV in a way that makes sense; careful about the measurement Basic experimental design One i.v. two levels o Experimental group Aka treatment group encounter some experimental stimulus o Control group Doesnt receive any experimental stimulus But in all other ways, the control group is exactly like the experimental group One d.v. o Gets measured Ex) testing a drug experimental group gets the drug; control gets the placebo with same shape etc; DV = whatever health outcome theyre measuring o Everything else is exactly the same o Ppl who are testing, dont know whos in which group o One IV with 2 levels with one DV very basic experimental design Pretest- posttest design You already have a post-test = measurement of the dependent variable Pre-test = measurement beforehand b4 you start doing anything
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