We are going to perform a t-test for independent means on these numbers. Our research hypothesis will be that the white students outperform black students on the MCAS exams to a significance level of .05. The null hypothesis is that white students do not outperform black students on the MCAS exams to a .05 significance. We know that if the null hypothesis is true, the two populations will have equal means and the distribution of differences between the means also has a mean of zero. In a t-test for independent means we average the estimated variance of both populations (since these should be estimates at the same number). The variance is "the sum of squared deviation scores divided by the degrees of freedom" (Aron & Aron, 2003, p. 231). The mean for black students is 48.5 and the mean for white students is 79.25. Calculations are as follows:
6.25 + 30.25 + 72.25 + 132.25 = 241 / 3 (degrees of freedom for "4" students) = variance of 80.33
3.06 + 39.06 + 18.06 + 76.56 = 136.74 / 3 = 45.58
Averaged variance 80.33 + 45.88 / 2 = variance of 63
We don't need to do a weighted average because or number of students is the same in both groups. The variance of the distribution of means is s²pooled / N which in this case is 4 so 63 /4 = 15.75. S²difference = 15.75 + 15.75 = 31.5. Taking the square root to get the standard deviation of the distribution of differences between means gives us 5.61. For our result to be significant with total degrees of freedom of 6 (3 for the white students plus 3 for the black students) and a .05 significance level for a one-tailed test (since our hypothesis was clearly directional), we use a cutoff score of 1.943 standard deviations above the mean of 0. Our t-score is the difference between the two sample means 34.75 divided by the standard deviation of the distribution of differences between the means or 5.61, which equals 6.19. This means our t-score is above the 1.943 cutoff score, and our results are clearly significant. The null hypothesis is rejected and the research hypothesis that whites outperform blacks on the MCAS exams is supported by our results. This information could be used to support a research study on how to improve outcomes for African-American students on the MCAS exams, working towards the ultimate goal of giving all students an equal education both in writing and other subjects as well.
References
Aron, A. & Aron E. N. (2003). Measurement, Evaluation, and Ethics in Research.
Pearson Custom Publishing: Boston.
Horn, C. (2003). High-stakes testing ad students: stopping or perpetuating a cycle of
failure? Theory into Practice, 42(1), 30-41.
Published by Galena Ojiem
My name is Galena and I am a stay at home mom of two gorgeous boys -- Gregory, who is a very exuberant 5-year old and JJ who is a very hungry 1-year old! I hope you enjoy my articles! :) View profile
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