ch. 2_083110 - Discussion Section PSYCH 227 08/31/10...

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Discussion Section PSYCH 227 08/31/10 Frequency distributions, central tendency, and variability Frequency Distributions Frequency distribution : a table showing the number of individuals located in each category or score on the scale of measurement. o What is it good for? Organize and summarize the data. Ungrouped frequency dist. : data are sorted into classes of single values Grouped freq. dist.: data are sorted into classes of more than one value Ungrouped F.D. example: 7,5,8,7,4,7,6,9,8,6 X (Score) f f*X p = f/n (relative frequency) % c.f. %c.f. 9 1 9 1/10 10 10 100 8 2 16 2/10 20 9 90 7 3 21 3/10 30 7 70 6 2 12 2/10 20 4 40 5 1 5 1/10 10 2 20 4 1 4 1/10 10 1 10 ∑f=n ∑(fX)= ∑X To build the distribution: 1. Sort scores from high to low. 2. Count the frequency of each score 3. Multiply X by f 4. To find p (proportion), divide f by n for each score (total should add up to 1) 5. Multiply p by 100 to find % (total should add up to 100%) 6. Start from the lowest score and add up f to get the cumulative frequency 7. % C.F. = c.f./n (TOTAL) *100% We can find n (sample size) by summing the f column. We can find ∑X by summing up the f*x column n = 10 ∑X = 67 Rules for building a grouped F.D. (use data from example 1 in handout) 1. We should have about 10 class intervals 2. The width of the intervals should be a simple, “nice” number. 3. Bottom score in each class interval is a multiple of the interval width 4. All intervals must be the same width and cover the entire range of scores. There cannot be gaps between the intervals.
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Step 1: find the range of scores by subtracting the lowest from the highest score in the data set. 3.78 – 2.25 = 1.53
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ch. 2_083110 - Discussion Section PSYCH 227 08/31/10...

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