Study Design

So, you want to do a study…how do you decide where to sample, what to sample and when to sample? While there are sometimes practical considerations that drive these decisions (need road access, want to do a study in your forest, etc.). The primary things that drives what, where and when you sample are the questions you are trying to answer. Here is a check list that may be helpful as you begin the process of designing a study.

1. What are the objectives of the study?

There may be multiple objectives for your study, if so then describe them and be sure they are compatible. For example, you may have…

  1. Educational objectives, such as introducing students to the scientific method or learning about forest ecology.
  2. Scientific objectives, such as describing the earthworm and plant populations in a particular habitat, or comparing the earthworm or plant populations in different habitats.
  3. Personal objectives, such as having fun or finding out which exotic earthworms are present in my forest.

2. What limitations do I have for this study?

While it’s nice to think big, but sometimes reality kicks in. It is important to know up front what your limitations are. For example, how much time do you have to do the study? What time of year do you need to do the work? How much , if any, money do you have to pay for the needed supplies? What is the expected skill and interest level of your group? You get the picture.

3. What are some targeted questions that can address the stated objectives?

Given your objectives and limitations, come up with a list of interesting questions that you think you could tackle and that may be particularly interesting for your site. For example,

  • What species of earthworms are present in my study site?
  • What species of plants are present in my site?
  • Does the species composition or biomass of the earthworm population change as I move from the lakeshore into the forest?
  • Would I get different results if I sampled earthworms using hand sampling vs. liquid extraction?

4. Determine what you will actually measure!

Different questions will require that you measure different things and it’s important to be clear that you are making the right measurement for the question being asked. For example, to answer the question “What species of earthworms are present in my study site?”, you need only use a method that generates a complete species list such as the “Flip & Strip” method. However, if your question was “What is the species composition and biomass of earthworms in my site?” then you need a method that measures both the species and the biomass present in a site, like “Liquid Extraction” (see earthworm sampling methods for more details)

5. Determine how you will sample your object of interest.

Now that you know the objectives, questions asked and what you need to measure, you can determine how and where you will sample the organism(s) of interest. You will need to use methods and sample plots that are appropriate for the object of interest.

6. Determine where you will sample your object of interest.

Generally, the goal of doing a study is to determine the average condition for a given site. Since you cannot sample every square inch of your study site, you need to use sample plots. You could select the sample plot locations arbitrarily (hey, this looks like a good spot!), and if you are doing a study to simply get a feeling for what is there, that can be fine (scientists call this “qualitative data”). But if you want use your data to answer a more specific question, you may want “quantitative data” that you can say with more confidence actually represents the conditions at your study site. To get “quantitative data” you would want to use some kind of sampling strategy. Two sampling strategies commonly used include locating your sample plots randomly or along transects.

Contact us with specific study design questions. We will be happy to help.