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Unformatted text preview: Statistics!!! On a 1-10 scale... How comfortable are you with your knowledge of statistics? scared out of your mind 1= 10= I do statistics in my spare time and love them How we are going to use stats To understand how to demonstrate the results of our studies To show the links between methods and stats = METHODS DRIVE STATS CONCEPTS!!! To write them in your papers How we are NOT going to use stats Endless only formulization-- for concepts Calculation-- Will not be running SPSS or SAS programs Though we will show you the basics Methods Today: Talk a bit about sampling, variables, measurement Descriptive statistics For the next few lectures: Begin thinking about how we might look for statistics within the studies you are writing/proposing at Inferential statistics Look Why Statistics? To characterize and quantify the differences in your sample = descriptive statistics examine what you find in your particular sample can be generalized to the population = inferential statistics To Statistics Will discuss two kinds
in both methods and results Descriptive
Will appear only in results Impact be explained in the discussion Descriptive Statistics DESCRIBE DESCRIBE your sample the results of your study in your sample what kind of data transformations you might make (e.g. DESCRIBE z-score) Descriptive statistics What kind of things can you report: Central Tendency Mean = Average Median = Midpoint Mode = Most common answer Some data
A group of individuals go out to a party and drink. Their number of drinks consumed are as follows:
# of drinks (x): 4 4 5 7 12 Central tendency Mean: M = (4+4+5+7+12)/5 = 6.4
average of the values Arithmatic Median: When Mdn = 5 the values are listed this is the exact middle value, has nothing to do with math Mode: mode = most frequently occurring value Mode =4 Descriptive Statistics Variability Range
difference (how different)
between highest and lowest score Standard
difference within a single sample Minimum value Maximum value What is? Range Min? Max? (highest lowest)?
# of drinks (x): 4 4 5 7 12 Standard Deviation SD = 1.88 Standard Deviation, the average difference around the mean How to calculate SD
1. Compute the difference between the values and the mean
1. 2. Mean is 6.4... So... 4 6.4 = -2.4 4 6.4 = -2.4 5 6.4 = -1.4 7 6.4 = 0.6 12 6.4 = 5.6 How to calculate SD
1. Square the differences
-2.4 * -2.4 = 5.76 1. -2.4 * -2.4 = 5.76 -1.4 * -1.4 = 1.96 0.6 * 0.6 = 0.36 5.6 * 5.6 = 31.36 Sum the squares and divide by the # of scores minus 1 45.20/ (5-1) = 11.3 1. The result of # 3 is the variance Variance is the spread of scores about the mean Variance is 11.3 in our sample 1. The square root of the variance is the standard deviation (SD) SD = 3.36 Example: Participants 100 section participants were randomly selected from a sample of high school students. Mean age was 14.4 years (SD =1.2). Average grade point average was M = 3.1 (SD = .75, min = 1.2, max = 4.0). 1 presents the average test scores by subject (See Table 1). Table Table 1: Average test scores by subject
Subject Percentile score 55 60 20 SD Reading Math Science
Note: n = 50 5.6 6.6 5.0 ...
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This note was uploaded on 08/26/2009 for the course BB H 310W taught by Professor Saltsman,brian during the Spring '07 term at Pennsylvania State University, University Park.
- Spring '07