# Feedback from trial session

Hi Declan,

I had 3 high school students at our skull measuring session yesterday. We encountered a few issues and the students struggled a bit with the conversion, but by the end we had a established a routine which we think worked well. Here is some feedback from our experience:

- The students had looked over the written procedures beforehand, but as we discussed the conversion calculations, it was clear they didn't understand it. So I rearranged the calculation to look like a more typical conversion calculation:
- [math]length\ (cm) = length\ (photo\ units) * \frac{ruler\ length\ (cm)}{ruler\ length\ (photo\ unit)}[/math]
- I decided to use "photo units" as the units, as we were measuring using computer drawing tools and it was unclear how the supposed inch measurements worked. We had two different laptops and the measurements (listed as inches) came out different, more than would be expected through measurement error.

- After going over this conversion formula, the students still didn't seem to get it, so I compared the conversion to converting inches to cm using the same set up:
- [math]length\ (cm) = length\ (in) * \frac{1\ (cm)}{2.54\ (in)}[/math]
- One girl still wasn't sure, but as we progressed I think she became more confident in her understanding.

- The students did not have open office on their laptops, I figured this would be the case and wrongly assumed that powerpoint would give the length of the line. We looked and looked and couldn't find it. But even before we decided the actual length was not available, only the x and y displacement, the kids had figured out they could use the pythagorean theorem with the x and y to get the hypoteneuse of the right triangle. Good solutions on their part.
- The plan was to create a google spreadsheet with the data from the measurements. We started out with 4 variables: ID, state, width and length. As you can imagine from what I've said, we ended up needing many more variables, x and y compenents for each skull measurement, along with x and y components for each ruler, and then the calculations for the hypoteneuse for each and then the conversion to length cm and width cm. I had to help the students with this part as they were a bit overwhelmed with how to set it up.
- We only had time to complete measurements on a few skulls. We meet again in two weeks and if there's interest, we'll continue the task....two students were absent yesterday, and it'll be useful to have the kids who were present explain how to do the measurements to the two who were absent.
- We measured skull 209 twice, as your measured length was provided in the instructions: 18.22 cm. Our first measurement was 19.85. Our second measurement was 17.94...which seemed more reasonable. Offers a good opportunity to talk about measurement error. I wonder if different measurement procedures generate more error than others.
- I wondered if we would get better measurements if we had a larger photo image. One of the students started to make it bigger, but when I commented that she needed to be careful to keep the same aspect ratio, she decided to use the smaller image.

Just some thoughts for consideration. Thanks for the opportunity to do some biology-related measuring. If we get measurements on a few more skulls, we'll try out some analysis procedures.

Alison p.s. I added our measurement results for skulls 209, 201, and 202 to the discussion tabs on the relevant pages.

Thanks Alison,

I just found your comments today. I remember why I have a hard time using the discussion threads....

I appreciate the input. I love the formulae you came up with. I'm surprised by the variability in the measurements. Makes me wonder if this approach is viable. I'll put a bunch of students onto this in my Spring course and see what sort of variability they come up with along with a comparison to original measurements.

The photos are about 3,000 pixels wide. I agree that greater precision can be achieved with a larger image. If the approach has a bias, there is no reason to expect the bias would create fake patterns...rather I'd expect either a consistent bias in one direction affecting all skulls, or increasing variance that would tend to obscure real patterns. My logic is that this is a conservative approach...if we find a pattern it's probably real.

In Spring I'll get 2 things going: more skulls; more measurements. Please thank your students for all their work. If they are interested in environmental data please let me know....land use..water quality....insect diversity. I have lots: http://www.uvm.edu/~streams/

Cheers, Declan

Hi Declan,

One way around the issue with notification of active threads on watched pages, is to activate LQTemail, under gadgets in my preferences. Been working consistently for me.

I can get back to this as well in the spring. I'll have a group of bio students exploring the ideas in evolution and a group of stats students learning about t-tests and ANOVAs.

Also, an idea which came from one of my students this year is whether there would be a difference in size between male and female skulls. Do you have this classification for the skulls? It would be useful, even if there tends to be no difference.

Hope you summer is going well.

Alison

I just activated LQTemail...better late than never; thanks for the tip

Re gender.....I have no idea. I get these from trappers so all I know with certainty is where the animals lived and died. There is an interesting thought though....if interested in regression with latitude; or pairwise comparisons, one could select the largest individuals from a given region...they will usually be male because the males are larger. This would decrease variance for large scale comparisons. CHeers Declan

Thanks Alison You are welcome of course! Thanks for the input. I used your suggestions to improve things and presented it all at the ABLE conference (Bio Lab Educators). I had the educators at the meeting make measurements from a sample of the largest NE and largest NW skulls and take it from measurement through stats (aimed at upper level college). We did on paper measurements or used ImageJ. If you print the ruler with each skull you can use the paper ruler to measure things (only for the skull that the ruler came with).

Here is the sample we worked with: http://wikieducator.org/NE_NW_skull_comparison Might be better for high school to start with a question where you already know the answer? NE>NW

I just read that coyotes from NW have shorter snouts....something for my Evolution kids in Spring to investigate. I expanded my Alaska and Texas collections so if there's a difference we'll find it

Cheers

Declan

Hi Declan,

Great idea to pick out sample with a known result, that we could work on from measuring through to statistical comparison. I have two kids in both my biology and statistics classes, so I'm hopeful that they'll be interested to follow through with the whole process. I'll definitely use the selected sample. We'll be tackling this in May or so. I'll check back here with how we make out.

Best, Alison