[SOLVED] BIOL 100 Experimental Design Basics

BIOL 100 Experimental Design Basics

Experimental Design: Hypothesis, Variables, and Groups

When using the scientific method, we get to a point where we formulate a hypothesis and then design an experiment to test that hypothesis.  Here are some pointers on this process.

The hypothesis states a special relationship between an independent variable (X) and a dependent variable (Y). A generic hypothesis is a statement that looks like “If I do X, I will see a measurable change in Y.”  Basically, the hypothesis looks like a statement of “cause” and “effect”. Your hypothesis is a direct statement and is not written in the form. of a question.

Remember that the independent variable is “what you do”, the dependent variable is “what you measure”.  

Let’s use a drug study to create a specific example of what a hypothesis should look like, and to see good examples of independent and dependent variables. Drug studies are usually straightforward.

A pharmaceutical company designed a drug (drug X) to treat migraine headaches (MH).

For this experiment, the hypothesis is “If I give drug X, patients will experience a reduction in migraine headaches (Y= # of migraine headaches/month).”

Drug X is the independent variable (what you do or give in the experiment), and the number of MH’s/month is the dependent variable (what you measure, where you see the result in the experiment).

Subjects (participants) in experiments are organized into either a “control” or an “experimental” group.  The subjects should be randomly assigned to one or the other.

First, we need a large pool of people who suffer with MH, and we randomly assign these people into two groups.  These groups should be IDENTICAL in every way– average age, same number of male and female, same average number of MH’s per month, same exercise levels, etc. All these variables that are equal – age, health, diet, are called “controlled variables”.

One group will remain the same throughout the experiment – the control group.  They get placebo pills.  The other group will get drug X, and they become the experimental group. 

Drug X is the ONLY variable that now makes the 2 groups different.  This is important, for when we measure the average number of MH’s per month in both groups, and we see a difference in the experimental group, only one variable, (X), can be associated with that difference. 

That leads us back to the hypothesis, “If we introduce X, we will see a change in Y.”