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Published byCalvin Lang Modified over 9 years ago
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1 Testing Statistical Hypothesis Independent Sample t-Test Heibatollah Baghi, and Mastee Badii
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2 Example of Independent Groups t-tests Suppose that we plan to conduct a study to alleviate the distress of preschool children who are about to undergo the finger-stick procedure for a hematocrit (Hct) determination. Note: Hct = % of volume of a blood sample occupied by cells.
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3 Example of Independent Groups t- tests, Continued Twenty subjects will be used to examine the effectiveness of the special treatment. 10 subjects randomly assigned to treatment group. 10 assigned to a control group that receives no special preparation.
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4 1. Determine the Appropriate Test Testing hypothesis about two independent means (t-test) –Dependent variable = the child’s pulse rate just prior to the finger-stick –Independent variable or grouping variable = treatment conditions (2 levels)
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5 1. Determine the Appropriate Test Two samples are independent. Two populations are normally distributed. The assumption of homogeneity of variance. (Examine Levene’s Test) H o : 1 2 = 1 2 H a : 1 2 1 2 If sig. level or p-value is >.05, the assumption is met.
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6 2. Establish Level of Significance The convention α =.05 α =.01 α =.001 In this example, assume α = 0.05
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7 3. Determine Whether to Use a One or Two Tailed Test H 0 : µ 1 = µ 2 H a : µ 1 µ 2 –Where –µ 1 = population mean for the experimental group –µ 2 = population mean for the control group
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8 4. Calculating Test Statistics Group 1Group 2 1100105 2 86 95 3112120 4 80 85 5115110 6 83100 7 90115 8 94 93 9 85107 10105120
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9 Rearrange the Data 11001 2 861 31121 4 801 51151 6 831 7 901 8 941 9 851 101051 111052 12 952 131202 14 852 151102 161002 171152 18 932 191072 201202 Experimental Group Control Group
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10 4. Calculating Test Statistics (continued) Group 1 (Experimental) Group 2 (Control) -------------------------------------------------------------------------------------------------- X1 X2 ------------ --------------
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11 4. Calculating Test Statistics (continued)
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12 6. Compare the Computed Test Statistic Against a Tabled Value
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13 6. Compare the Computed Test Statistic Against a Tabled Value If we had chosen a one tail test: –H 0 : µ 1 = µ 2 –H a : µ 1 < µ 2 1.73 The null hypothesis can be rejected
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14 SPSS Output for Two Sample Independent t-test Example
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