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Psyc_315_-_Winter_2010_-_Class_23

# Psyc_315_-_Winter_2010_-_Class_23 - Independent Samples...

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1 Independent Samples t-Test Practice Problems 2 Example 1 A psychologist prepares a list of 40 pairs of nouns. 2 groups of 10 participants are obtained. Group 1 is given 5 minutes to memorize the list, and are also told to form mental images of the words. Group 2 is only given 5 minutes to memorize the list. Later, each group is given a memory test in which they are given the first word of each pair and asked to recall the second word. The number of correctly recalled words for Group 1 are 19, 20, 24, 30, 31, 32, 30, 27, 22, and 25, whereas for Group 2 are 23, 22, 15, 16, 18, 12, 16, 19, 14, and 25. Can the psychologist conclude that mental images increase memory? (use alpha 0.05) 3 Answer to Example 1 =200/9 S 2 1 =22.22 X=260/10 M 1 =26 1 -1 25 16 -4 22 1 1 27 16 4 30 36 6 32 25 5 31 16 4 30 4 -2 24 36 -6 20 49 -7 19 (X-M 1 ) 2 (X-M 1 ) Imagery =160/9 S 2 2 =17.78 X=180/10 M 2 =18 49 7 25 16 -4 14 1 1 19 4 -2 16 36 -6 12 0 0 18 4 -2 16 9 -3 15 16 4 22 25 5 23 (X-M 2 ) 2 (X-M 2 ) Control

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2 4 Answer to Example 1 Step 1: H 0 : M 1 M 2 ; H 1 : M 1 > M 2 Step 2: 9 (22.22) + 9 (17.78) = 20 18 18 20 = 2 10 20 = 2 10 2+2 = 2 Step 3: 26 – 18 = 4.00 2 2 2 2 1 1 2 2 ( ) ( ) pooled total total df df S S S df df = + = 1 2 2 1 pooled M S S N = = 2 2 2 2 pooled M S S N = = 2 2 1 2 M Difference M M S S S = + = 1 2 1 sample M M M t S difference - = = 5 Answer to Example 1 Step 4: t-critical (df = 18, p < 0.05, 1–tailed) = +1.734 Step 5: Beyond the critical boundary, therefore, reject the null hypothesis. Memory scores in the imagery condition are significantly higher than scores in the non-imagery condition.
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Psyc_315_-_Winter_2010_-_Class_23 - Independent Samples...

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