Control and variables

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Control and variables

Postby Tennbears » Wed Nov 07, 2012 8:30 pm

My daughter is doing her project on the decomposition of food-fresh vs processed. She is using a McDonalds cheeseburger and fries compared to a homemade fresh burger, real cheese, fresh bun and home cut fries. We will place both under two seperate glass domes to create a controlled atmosphere. Our variable is the fresh vs processed. What would we consider or use for the control? Is that the glass domed controlled atmosphere? I am not sure I understand this part. HELP! LOL
Thank you!
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Project Question: We are doing a project comparing the decomposing process between processed and non processed food. (McDonalds to a homemade burger and fries)
Project Due Date: 12-7-12
Project Status: I am just starting

Re: Control and variables

Postby edneu3 » Thu Nov 08, 2012 9:37 am


This is an interesting experiment, and one that should be really applicable to our every day lives.

The way your daughter has planned the experiment, by comparing one type of food to another, i.e. McD's vs fresh, she has already established one control. The fresh food would be the control to which she will compare the results of the McDs food.

You have a key idea about the controlled atmosphere. It is important to control as many variables as possible. To do this properly, she should monitor the temperature and humidity under each glass jar, and perhaps establish one other type of "control". If she could put one food item under each jar that was the same, like a piece of apple or some other food that is not in either of the test sample, then if the environments were controlled the same she should observe the same deterioration in the "control" food substance. If the control sample does not decompose in the same way, either the environments were not really the same, or something inside the glass dome affected the way the control food sample deteriorated.

One other thing to consider is that this experiment needs to be repeated multiple times. We can never form a valid conclusion from an experiment if we doi it just once.

And be sure she does some basic research. I did a quick scan of the internet and have a couple sites she should study: ... vation.htm ... ation.html

Good luck helping your daughter with this great project, and HAVE FUN!
Ed Neu
Buffalo, MN
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Re: Control and variables

Postby Craig_Bridge » Thu Nov 08, 2012 9:45 am

In general, A vs B comparision tests typically fall into a class of experiments that are "self controlled".

What is your hypothesis? The wording of your hypothesis MIGHT determine which of the food collections is the control.

CAUTION: From a scientific investigation validity perspective:
1) Only having TWO containers is a problem. Unless you utilize multiple supposedly identical samples and the results of all samples are in reasonably close agreement, you can't draw a scientifically valid conclusion because you have no data that indicates similar samples are expected to behave similarly. In other words, there maybe some undetermined factor in a particular sample that caused the results that is not expected to be present for all similar samples. At this grade level, three or five samples of each type would be appropriate.
2) Mixing multiple foods in the same container creates the possibility of undetermined interactions which could influence the result. Mixing french fries and a cheeseburger in the same container might yield a significantly different result than if those two foods were in separate containers. Cheeseburgers are multi-component foods so the behavior of any one component might dominate the results.

I recommend that you simplify the experiment and deal with only one food component. You then need to attempt to minimize the differences between your "fresh food" and "processed" samples. For example, size, shape, surface area, weight, need to be similar in order to eliminate those variables as potential causes for differences in outcomes.
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