Science Buddies: "Ask an Expert"

i am having trouble locating a definition for the four types of controls. can you help me?

Tom:

A control is a standard that all treatments are measured against. It can be positive (present) or negative (absent).

Back to your question - do these four controls have names?

Matt Mulanax

are there definitions for the four types of controls i listed?

if so, where can i find them?

Hi Tom,

I didn't see the 4 types of controls you listed, but here is additional information for controls that should help you with your science fair project.

A control is a sample with a known value. For example, if you were testing a variety of fruit juices for vitamin C content, your control samples would include a sample that did not contain any vitamin C (negative control) and one that did contain vitamin C (positive control). If you were testing a range of vitamin C values, it would be better to include two positive controls, one in the low range of your standard curve, and one in the high range. The results on the control sample verify that your test reagents are working correctly.

Another meaning of control, in a science fair project, refers to the experimental parameters. With a controlled experiment, for example, if you want to measure the effect of light intensity on plant growth, the only experimental condition that would vary would be the light intensity. The temperature, soil, moisture, plant, and all other experimental conditions would be identical, or "controlled."

Now, what are you doing for your experiment? Let us know why you are asking the question. I'm sure we could make some additional suggestions if you need more help.

Donna Hardy