IPS - Day 50

Today the class started to look at the idea of hypotheses.

First, I collected what work the students had produced for the chocolate experiment. I wanted to see where they were in their analysis and if they were attempting to include the requisite pieces. Since we'll be expanding on the work they conducted so far, I am treating this as a formative assessment.

Next, I showed students a statement about the "Big Idea of Inference":


Is what we observe happening different from what can happen by random chance, under the conditions of what we believe to be true (our assumptions)?

We discussed what this meant. Students asked some clarifying questions. There was a good discussion between two students about what was meant by conditions we believe to be true. Some students related this statement back to their experiences in science class.

With that, we took a look at the 39-game hitting streak investigation that we worked on previously. I asked students what results they had found for the mean hitting streak length. After writing some values on the board, I was able to point out that every time a new sample is generated, the mean for that sample may vary from previous sample means.

I asked students to use a scale of 1-100 with 1 being no confidence and 100 being absolutely certain, how confident were they of seeing a hitting streak of roughly 8 games? The class responded with values the tended to be between 50 and 80.

When asked what length hitting streak would you expect to see, students responded with values concentrated in the 3-15 range. They rated the likelihood of seeing a hitting streak of this length as quite high. Overall, the class responses were consistent with the data they observed.

I presented other questions of interest that could be posed for this scenario. This was to illustrate that one scenario could provide many different looks of the data.

Next, we covered the basics of inference. I pointed out that they were accomplished on some aspects but there were other aspects that we needed to develop. In particular, the class needs to develop an understanding of hypotheses and how to use their analysis to draw a conclusion about their hypotheses.

The next step was for students to attempt to develop a null hypothesis. This required them to think about the assumed values, what they wanted to prove, and what they could disprove. This is a hard concept initially, because the tendency is to create a null hypothesis about what you want to show and the alternative to be what you don't want to happen.

I explained to the class, you either lack data to reject the null hypothesis or you have data that is inconsistent with the null hypothesis, which you then reject. It is akin to someone charged with a crime. Either evidence shows that the person is guilty or the evidence is inconclusive and the person is found not guilty. The verdict of not guilty does not proclaim that someone is innocent, only that there was not enough evidence to demonstrate the person's guilt.

For a first attempt, students actually did quite well with writing their null hypothesis. Some students wanted to keep their hypothesis in the form of a question and others had the null and alternative hypotheses reversed.

We discussed several null hypotheses that were written and then proceeded to look at the alternative hypotheses that were created. At this point, more students were comfortable with creating the opposite statement to their null hypothesis.

I gave the class a second question of interest and this time the creation of null and alternative hypotheses went faster and were much more consistent across the class.

Time was running out. I projected an excerpt from a local newspaper article and asked the class to write a question of interest and to create null and alternative hypotheses for their question. We'll look at what they produced next class.


Visit the class summary for a student's perspective and to view the lesson slides.