Behavioral Variability January 13 2016 Variability in Psychology Psychologists are interested in studying how and why behaviors thoughts and emotions vary o Across situations a Saturday Your behavior is much different in class vs when you go out on Our behavior varies depending on situations in our lives Pavlov experiment studied how behaviors in dogs changed when the bell was present vs not o Among individuals o Over time Willingness to answer questions in class for example Developmental psychology focuses on this Behaviors vary from infancy through adulthood How do relationships change over time Satisfaction change over time Why are people more aggressive than others Why does aggression vary among individuals o Parenting modeling their behavior o Biological factors Testosterone o Exposure to violent TV video games etc o Genetics in our DNA Why do partners become unhappy with their relationships Why does satisfaction vary over time Across individuals o Stressors o Life challenges o Communication o Disliking qualities about your partner over time o Loss of attraction o Children Describing Variability To understand variability we need statistics Conceptually o How much variability do we have o Example used in class hours slept last night o Range Difference between the lowest score and highest score Average of a set of scores o Mean o Variance Graphically o Histogram Charts scores by frequency Frequency on the y axis Hours slept on the x axis Calculating Variance The sum of the extent to which points deviate from the mean Step 1 Calculate the mean o Score 1 score 2 score n n Step 2 Subtract mean from each score o Deviation score Step 3 Square the deviation scores o Because some are negative and some are positive Step 4 You must divide by n 1 o The more people we have the bigger the total sum of squares we have o Variance S2 Statistical Notation S2 yi ybar 2 n 1 o yi each individual score o ybar mean Mean formula in stat notation o yi n o yi each individual score o n sample size how many How is mean useful for variance Gives us a standard to compare data o How much do we vary from this standard In class Example Use the following set of all self esteem scores provide both range and Scale variance January 20 2016 Highest self esteem 10 Lowest self esteem 1 1 7 3 4 6 5 5 7 6 6 Range 7 1 6 Variance Step by step 1 Find the mean 1 3 6 5 6 7 4 5 7 6 10 50 10 5 2 Subtract the mean from each individual score 1 5 4 7 5 2 3 5 2 4 5 1 3 Square all the numbers 16 4 1 1 4 Add all of these numbers together 0 4 4 1 1 0 6 5 1 5 5 0 5 5 0 7 5 2 6 5 1 6 5 1 32 4 Divide by n 1 n 10 n 1 9 32 9 3 56 Always round to 2 decimal places APA Style Types of Variance Systematic variance o Variance in the dependent variable associate with the independent variable s o Example Variability in academic performance and SAT o What else can account for academic performance IQ GPA Prior schooling public vs private Time management skills Study time o There are a lot of things that predict our behavior o SAT scores is the systematic variance in this example o Everything else mentioned above is Error variance o Variance in the dependent variable NOT associated with the independent variable Not mistakes in this case error does not mean a mistake it means variable due to something other than the independent variable Unmeasured variables Where Statistics Come In Statistics help researchers determine what variance is systematic variance and what variance is error variance Not only do we want to know IF there is a relationship but we are also looking for How strong is that relationship if there is one o Effect size Tells us the strength of the relationship o The more variability is systemic the stronger the relationships between the IV and the DV o The bigger the piece of the pie proportion of the total variance the stronger the relationship o This is known as the proportion of variance
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