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Controlling Variance Variance can cause misinterpretation of the results Variance is found in the population under study 4 ways to control variance: Randomization Building in factors as IVs Holding factors constant Statistical control
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Randomization Random selection, or assignment, of subjects spreads the effect of whatever is causing the variance, evenly across the participating groups. Teacher/ Curriculum A 50 students randomly assigned to Group 1 Performance on a geography test Teacher/ Curriculum B 50 students randomly assigned to Group 2 Performance on a geography test Teacher/ Curriculum C 50 students randomly assigned to Group 3 Performance on a geography test Study comparing curricula A, B, & C
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Factors as Independent Variables Include factors causing variance as independent variables in the study. Curriculum A Curriculum B Curriculum C High Ability Low Ability High Ability Low Ability High Ability Low Ability 25 students Geography test Study comparing curricula A, B, & C
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Holding Factors Constant Reduce the influencing factor (or variable) to a constant. Curriculum A 50 Low Ability students ran- domly assigned to Group 1 Performance on a geography test Curriculum B 50 Low Ability students ran- domly assigned to Group 2 Performance on a geography test Curriculum C 50 Low Ability students ran- domly assigned to Group 3 Performance on a geography test Study comparing curricula A, B, & C
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Let’s Try One The researcher is seeking to determine the effects of two different cohort programs on a heterogeneous sample of educational administration students at California State University. Sample: 100 students 1 st & 2 nd year White, African American, Southeast Asian, Latino/a All have 3 – 5 years teaching experience Cohort Programs Urban Leadership Emphasis Bilingual Leadership Apply the Holding Factors Constant strategy to the study.
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Now You Try It! What is the best way to teach 5 th grade students who are reading below grade level in Sacramento schools? 1. Describe the population. 2. Identify one factor that may cause variance. 3. Describe 3 samples, using each of the first 3 strategies to control variance. Post your responses to WebCT under the forum, HW 7.
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