psych301 study ch-2

psych301 study ch-2 - Chapter 2 Behavioral Variability and...

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Chapter 2 Behavioral Variability and Research Key Terms Descriptive statistics Inferential statistics mean range variance standard deviation deviation scores Sum of Squared Deviations (aka, Sum of Squares, SS) Total variance Systematic variance Error variance Total SS Systematic SS Error SS
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Descriptive statistics These are used to describe or summarize some behavior or characteristic of a group of people. For example, what is the average ACT score of incoming ISU freshman? How tall is the average NBA center? How much do starting salaries of new college graduates vary? Of high school seniors in rural Iowa, how many have never been drunk? How many have been drunk once? How many have been drunk more than once? Inferential statistics In research, inferential statistics are what we use to make decisions… or to decide what conclusion we should make about the results of a study. For example, do Iowa elementary school students score more highly on reading tests than the rest of the nation? Does increasing the room temperature make people behave more angrily toward each other? Does GPA predict future salary? Inferential statistics allow us to decide whether the relationship between two variables (or the difference between two groups of people) is big enough that it is very unlikely to have occurred just due to the chance differences that always affect results in research. If we did not have statistics, then we could not make much progress because researchers with different points of view would argue about whether a relationship or difference was really meaningful, or whether it was just due to a random fluctuation. Some statistics Mean – the mean is the average, and it is really easy to calculate. You just take all the numbers, add them up, and then divide them by how many numbers there are. So, if you measure 5 people on some variable called y, and the 5 values of y are 2, 7, 1, 12, and 2, then the mean is just (2 + 7 + 1 + 12 + 2)/5 = 24/5 = 4.8 Range – the range is kind of tricky, because people think of it in terms of the actual numbers. For the five values of y given above, it would be WRONG to say that the range of y was 1 to 12. The CORRECT answer is that the range is 11. The range is calculated by subtracting the smallest number from the greatest number. So, 12 – 1 = 11. Be careful of negative numbers. If we had four numbers, 5, 1, 0, -4…. the range would be 9, which is the result of subtracting the smallest number (-4) from the biggest number (5). Deviation score – this is another easy thing to calculate. For each value of y, you see how much it deviates from the mean of y. So, for y=2 with a mean of 4.8, the deviation score is 2 – 4.8 = –2.8. For y=7 with the mean still being 4.8, the deviation score would be +2.2. If you add up the deviation scores for all the numbers that went into calculating a mean, the sum must be 0. That little fact is important to know. Variance – The variance is a measure of
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psych301 study ch-2 - Chapter 2 Behavioral Variability and...

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