2009/11/30

Journal Entry #10

This was my last observation in the class which review sample distribution and use of confidence intervals on calculators. I tried to distinguish clearly metacognitive processes of the teacher and students. While Ms. Ringquist was lecturing on sample distributions by using technology (screening on the white board), the students were paying attention in order to process information presented. Other topics included Central Limit Theorem and taking sample averages, both already covered. Ms. Ringquist gave them always enough time to copy from the white board, but not too much so that they could lose their attention. The students were not interacting a lot with the exception of participating during the lecture. Therefore, they were happy to play the Greedy Pig in the middle of the lesson. Another exam is approaching and therefore no new material was explored today and the students had time to work through homework examples.

The example of sample statistics, for example, revised the standard error idea and the confidence interval. If the confidence interval is exactly 95%, the multiple of standard deviation is not 2 but 1.96 (because of the shape of Normal distribution). Therefore, I found it very interesting to solve an example illustrating that, in order to have 3% margin of error (1.5% to each side of a mean value) for big sample size, it is necessary to chose the sample size of 1,068 at most. This example was presented through an application of presidential elections. If each candidate has certain probability to be elected (and the is the chance to be not elected), and if that is 0.5 (so the product with the other probability is the biggest possible, i.e. 0.5×0.5=0.25), then by the definition of standard deviation, sampling large samples and confidence intervals, it is enough to ask a sample of 1,068 random people to be 95% sure about the 3% interval for the event of being elected. Up until now, I was wondering why back home in Slovakia statistic companies always used a (somehow magic to me) number 1,068. And here the explanation was. J

Overall, I would say that this revising lesson had a pretty standard format the teacher, students and even I are used by now – revision of main ideas presented by the teacher and then students’ questions about previous homework examples. It is for sure that this lesson was not designed to engage students by its activities, but rather by the content presented that is interesting enough to think about.