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01_Oneway1

01_Oneway1 - Experimental Design as a Research Strategy …...

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1 Experimental Design as a Research Strategy " … . A plan for assigning subjects to experimental conditions and the statistical analysis associated with the plan." (Kirk, 1995, p.1) • What makes experimental research distinctive from other research strategies? • This course concerns: • The plan or assigning subjects to experimental conditions. • The statistical analysis for the plan. • This course assumes: • Equal number of subjects in all treatment conditions. The Logic of Hypothesis Testing • Hypothetical Example (two-sample t -test) § = 117, = 125, and n 1 = n 2 = 31 § Question: “Are the means significantly different?" § The null hypothesis and the alternative hypothesis; H 0 : μ 1 = μ 2 H 1 : μ 1 ≠ μ 2 § Results t = 1.25, df = 60, p = 0.108 1 X 2 X

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2 Interpretation of p -value A small p -value indicates that the obtained statistic is unusual, under the assumption that the H 0 is true. The smaller the p -value, the more the data support rejecting the H 0 . More formally, p -value is the probability of observing the size of effect from the data or larger , when H 0 is actually true. In practice, you reject H 0 when the p -value is smaller than a predetermined α -level. (In the example) • Predetermined α = 0.05 • Then, not reject the H 0 , because p is larger than 0.05. • Conclude that the means are not significantly different. Another method of hypothesis testing is to compare the obtained statistic and a corresponding critical value, without computing the exact p -value.
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01_Oneway1 - Experimental Design as a Research Strategy …...

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