Thursday, December 15, 2011

Scientists don't just learn from experiments!

If I ask students what a scientist does, they often answer "Do experiments!".  That is true of many scientists, but many great scientists have learned a lot without doing any experiment at all.  In my research I use experiments and something we call an observational study.
What is the difference between an experiment and a study?

Scientists often use controlled experiments and observational studies. There are many types of controlled experiments, but in general, the scientist will select a group of study subjects, randomly assign them to different treatments (or conditions where a variable is altered). It is important that the scientist is changing something about the conditions the study subjects will experience.   In an observational study, the scientist does not alter anything about the study subjects, but just makes careful observations and draws inferences.

Lets use an example to demonstrate the difference.  Suppose you have the question, Does temperature determine whether a turtle egg will become a male or female?  

Observational Study: You go out into the wild, and locate lots of fresh turtle nests from the same population, and monitor these nests until they hatch.  It would be best to record temperatures throughout the season within the nests, as well as other variables you think might be important (hydric conditions, soil pH, etc).  When they have hatched, you correlate the environmental variables with the sex ratio of the baby turtles in each nest.  Depending on what you find, you may want to repeat the study another year, or you may want to then further investigate these relationships in an  controlled experiment.
In the photo above, we are measuring various aspects of a natural painted turtle nest, as a part of a long term study started by my advisor Fred Janzen.  Who knew studying could be so fun!!  Photo by Brian Tugana.

Controlled experiment:  After collecting lots of turtle eggs from many moms in the same population of turtles, you can randomly divide the eggs from each mom into two treatments, warm and cool.   You set up two incubators at a cool temperature, and two at a warm temperature.  In this case, temperature will be the independent variable, or the thing the experimenter varies.  Then we need controls: all the eggs will be incubated in boxes that have the same substrate, the same water potential, the same amount of eggs in each box, etc.   After eggs hatch, you can see if the treatment (temperature) had an effect on the sex of the baby turtles.

To thoroughly answer this question, it would be best to do both this experiment and the study, as both give you different and important information.

Here we are measuring baby turtles in a lab.  These turtles were a part of one of my experiments! Most of this experiment took place in the field, but some parts happened in the lab.  Just because its an experiment, doesn't mean it needs to be in a lab.

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