Guided Practice: What activities or exercises will the students complete with teacher guidance?
This activity will simulate an infection network between students in a given population. The suggested population is an entire grade level. Students will pass an object among themselves and record the name of the person who gave them the object. The record logs containing the names will be collected and processed (by the teacher or responsible students) to create a visual graph of the network. This may be an extra credit opportunity for a responsible student. Students will evaluate the quality of the network data they generated and collected and will understand how their network was created by examining the resulting visualization. Students will discuss the potential for error in data collection, reporting, and evaluation.
Each student in the population must be informed of the lesson. This is important for situations where there are multiple teachers for a subject within each grade. A coordinated effort among the subject teachers for a particular grade would allow for all students to be aware of this grade-wide activity. For restricted populations (such as single class or single teacher), students must be aware that their non-population classmates will not be participating and all lesson-specific activity must occur only with students in their immediate population.
- A series of identical 'infection cards' or other items to be passed around among the student population (if paper, the cards should be laminated for durability). The number of cards will affect the resulting graph. The number is to be determined by the teacher and this may be a point of study if one is interested in comparing network results by varying the number of cards. The recommended starting number is three cards. These design of the card is at the discretion of the teacher but the suggestion is to make them look interesting and brightly colored so they are fun but also so they do not get lost.
- A log sheet for each student. The log sheet contains space for the student name at the top and many lines below for recording the names of students that passed the card to them (students will record incoming infection events by writing the name of the person that 'infected' them).
There are several restrictions or rules for the activity that must be followed:
- Students must accept all incoming 'infection' events. If someone gives you a card, you must take it and write down their name on the log sheet. Teachers will reinforce the importance of accurate record-keeping and honesty in scientific endeavors.
- Students cannot return the card to the person who gave it to them last. This is not to say that they cannot ever give the card to that person, but they cannot return it to that person without passing it to a third party. For example, Student A gives the card to Student B. It is ok for B to give the card to Student C but B cannot return the card to A at that point. If the card comes back to B at some later time, it is permissible for B to give the card to A at that time. This rule forces the card to move within the population instead of simply moving back and forth between two individuals.
- If you find a card that was lost somehow, you must pick it up and continue with the activity. You must record the infection event and list the name as 'found'.
- Do not lose the cards. Return them to the teacher at the specified end of the activity.
This lesson activity will span, at minimum, one whole day after the lesson was introduced. This will allow time for the students to mingle and exchange the cards. It is recommended that students receive the lesson on Day 1 and spend Days 2 and 3 exchanging cards. Other instruction/lessons can take place while students work on this project 'under the radar'. On Day 4, students would turn in their log sheets. Some time will be needed to process this data, depending on the number of students. This processing can be distributed among students and teachers. After the data are processed, a graph is created using a computer program. The resulting graph is presented to the students and is discussed in a debriefing session.
This data processing will involve the creation of a computer file containing the information about the individuals in the network and their interaction with each other. This network will result in a 'directed graph' which involves a flow of information, association, or in this case, infection, from one individual to another. The resulting graph will indicate the direction of flow with arrows instead of non-directional lines. With this additional information, one can see the 'infector' and the 'infectee' for any connection.
The data from log sheets are to be converted to a ".GML" text file for processing. This can be done using a simple text editor like "Notepad" for PCs. Instructions will be given for this process using this text editor program, available by default on Windows-based computers.
- Gather all log sheets turned in by the students.
- Open Notepad and add the following example .gml file (type it or copy and paste):
node [ id 1 ]
node [ id 2 ]
node [ id 3 ]
Explanation of the code: The graph code opens with "graph" and an open bracket [. The graph later closes with a closed bracket ]. The first line of the graph notes that this is a directed graph with a 1. A zero (0) indicates a non-directed graph. The next section introduces all of the nodes (students in this case). Each receives an ID number. The following section describes the connections of the nodes. These connections are formally called 'edges'. To describe the connection, you must identify the source student (who had the card) and the target student (who got the card from the source). Each student must be listed with ID number and each connection must be listed. Depending on your data, this typing may take a while. To reduce the chance for error, it is recommended to create a template 'dummy' entry, copy/paste it as many times is as necessary, and then fill in the specific information from your data. Follow the example above, keeping all nodes described together first, and then describe all connections.
You may want to try this out with a very small set of data first before proceeding with the entire set.
When the typing task is complete, click File->Save As->, choose a location to save your file, and enter the name of your file in the File Name box as "myData.gml" (without the quotes). Beneath that, set "Save as type" to All Files. Click save to create the file.
This lesson utilizes a program called yED to construct the node graph. This program accepts data in the .gml file format as described above. The program can be run online or can be downloaded at the link below:
Information about yED
You may need to install Java to run yED. Information about checking to see if you have Java and installing it if you need it can be found at the link below:
Information about Java
It is recommended that you format the results for easy interpretation. The method presented below is a suggestion. Additional exploration of the yED visualization options is recommended.
Once you have yED running, go to File->Open and open your .gml file. Select the resulting set of nodes by clicking the screen and drawing a box around the data. They should become highlighted when selected. right-click the highlighted nodes and select Properties from the local menu. Here, you can change the shape if desired.
Next, go to Tools->Centrality Measures from the top menu. Under the General tab, make sure the Centrality Measure option is set to Number of Connected Edges. Under the Result Presentation tab, set the Size of the Most Central Node to 100 and the Least Central Node to 10. Set the Color of the Most Central Node to a darker color and the Least Central Node to a lighter color. These Centrality Measure options will change the color and size of the nodes based on the number of connections. This aids interpretation of the graph.
Finally, go to Layout->Organic under the top menu. Keep the default settings, and click ok. The graph should shift so you can see all the nodes and their connections.
To export the graph as an image, go to File->Export and choose a format for the file.
The teacher will present the resulting graph using a projector or document reader. Handouts of the network may be used as well but the network size may be a factor in text legibility if the entire network is fitted to standard paper size. A large poster print would be a useful tool if that is an option.
Classroom discussion will cover the usefulness of network graphs, visual modifications for ease of interpretation, direction of connections between students in the graph, the extent to which the entire population of students was involved in the final result, interpretation of the results, and factors that influenced the results.