Chances are you've heard of the scientific method. But what exactly is the scientific method?
Is it a precise and exact way that all science must be done? Or is it a series of steps that most scientists generally follow, but may be modified for the benefit of an individual investigation?
"We also discovered that science is cool and fun because you get to do stuff that no one has ever done before." In the article Blackawton bees, published by eight to ten year old students: Biology Letters (2010) //rsbl.royalsocietypublishing.org/content/early/2010/12/18/rsbl.2010.1056.abstract.
There are basic methods of gaining knowledge that are common to all of science. At the heart of science is the scientific investigation, which is done by following the scientific method. A scientific investigation is a plan for asking questions and testing possible answers. It generally follows the steps listed in Figure below. See //www.youtube.com/watch?v=KZaCy5Z87FA for an overview of the scientific method.
Steps of a Scientific Investigation. A scientific investigation typically has these steps. Scientists often develop their own steps they follow in a scientific investigation. Shown here is a simplification of how a scientific investigation is done.
A scientific investigation typically begins with observations. You make observations all the time. Let’s say you take a walk in the woods and observe a moth, like the one in Figure below, resting on a tree trunk. You notice that the moth has spots on its wings that look like eyes. You think the eye spots make the moth look like the face of an owl.
Figure 2: Marbled emperor moth Heniocha dyops in Botswana. (CC-SA-BY-4.0; Charlesjsharp).
Does this moth remind you of an owl?
Observations often lead to questions. For example, you might ask yourself why the moth has eye spots that make it look like an owl’s face. What reason might there be for this observation?
The next step in a scientific investigation is forming a hypothesis. A hypothesis is a possible answer to a scientific question, but it isn’t just any answer. A hypothesis must be based on scientific knowledge, and it must be logical. A hypothesis also must be falsifiable. In other words, it must be possible to make observations that would disprove the hypothesis if it really is false. Assume you know that some birds eat moths and that owls prey on other birds. From this knowledge, you reason that eye spots scare away birds that might eat the moth. This is your hypothesis.
To test a hypothesis, you first need to make a prediction based on the hypothesis. A prediction is a statement that tells what will happen under certain conditions. It can be expressed in the form: If A occurs, then B will happen. Based on your hypothesis, you might make this prediction: If a moth has eye spots on its wings, then birds will avoid eating it.
Next, you must gather evidence to test your prediction. Evidence is any type of data that may either agree or disagree with a prediction, so it may either support or disprove a hypothesis. Evidence may be gathered by an experiment. Assume that you gather evidence by making more observations of moths with eye spots. Perhaps you observe that birds really do avoid eating moths with eye spots. This evidence agrees with your prediction.
Evidence that agrees with your prediction supports your hypothesis. Does such evidence prove that your hypothesis is true? No; a hypothesis cannot be proven conclusively to be true. This is because you can never examine all of the possible evidence, and someday evidence might be found that disproves the hypothesis. Nonetheless, the more evidence that supports a hypothesis, the more likely the hypothesis is to be true.
The last step in a scientific investigation is communicating what you have learned with others. This is a very important step because it allows others to test your hypothesis. If other researchers get the same results as yours, they add support to the hypothesis. However, if they get different results, they may disprove the hypothesis.
When scientists share their results, they should describe their methods and point out any possible problems with the investigation. For example, while you were observing moths, perhaps your presence scared birds away. This introduces an error into your investigation. You got the results you predicted (the birds avoided the moths while you were observing them), but not for the reason you hypothesized. Other researchers might be able to think of ways to avoid this error in future studies.
The Scientific Method Made Easy explains scientific method: //www.youtube.com/watch?v=zcavPAFiG14 (9:55).
As you view The Scientific Method Made Easy, focus on these concepts:
- the relationship between evidence, conclusions and theories,
- the "ground rules" of scientific research,
- the steps in a scientific procedure,
- the meaning of the "replication of results,"
- the meaning of "falsifiable,"
- the outcome when the scientific method is not followed.
Dan Costa, Ph.D. is a professor of Biology at the University of California, Santa Cruz, and has been studying marine life for well over 40 years. He is a leader in using satellite tags, time and depth recorders and other sophisticated electronic tags to gather information about the amazing depths to which elephant seals dive, their migration routes and how they use oceanographic features to hunt for prey as far as the international dateline and the Alaskan Aleutian Islands. In the following KQED video, Dr. Costa discusses why he is a scientist://science.kqed.org/quest/video/why-i-do-science-dan-costa/.
Scientists conduct investigations for all kinds of reasons. They may want to explore new ideas, gather evidence or prove or disprove previous results. Although scientists must follow certain methods to ensure their results are fair and accurate, there are many ways they can conduct an investigation. Two aspects scientists need to consider are how big their investigation will be (small scale versus large scale) and how long it will run (short term versus long term).
Small-scale and large-scale investigations
To gain a better understanding of the concept of scale, consider an episode of MythBusters – the TV programme that uses science to test the validity of urban myths and internet videos. The MythBusters team often starts by building a small-scale model to test a myth. This allows them to gather data about the way their model works. If the small-scale investigation answers their questions, they go on to build a full-scale model. They do this to ensure the investigation is more realistic and the results are more accurate.
Dr Nicole Schon from AgResearch follows the same principle. She wants to know more about the role anecic earthworms play in carbon storage in pasture soils. To do this, Nicole puts carbon sources (plant litter and dung) on the soil surface. She uses differences in carbon isotopes to track its incorporation and distribution within the soil profile. (At an atomic level, carbon can have different forms with different atomic masses.)
Nicole’s investigation involves two components. The first is a smaller lab-based investigation set to run for a year. For this, Nicole established a number of microcosms – buckets of soil that simulate earthworms’ usual environments. Nicole is able to manipulate variables (such as the type of earthworm species) and make precise measurements of changes to carbon within the soil in each bucket.
Running alongside the microcosm experiments is a longer and larger-scale field investigation. Nicole has a number of field sites – intensively farmed pastures – where anecic earthworms were absent. She has introduced anecic blackhead earthworms (Aporrectodea longa) to these sites and allowed them to become established. Nicole periodically applies carbon sources (dung) to the soil surface. She uses carbon isotopes to assess the changes in carbon by removing a core of soil, analysing the contents and correlating it with the abundance of the anecic earthworms. The larger field investigations provide real-life conditions, and Nicole hopes they will confirm the microcosm experiments. The field sites will also provide information on how the A. longa species becomes established and how it spreads. If they are found to incorporate large amounts of carbon, the goal will be to introduce A. longa earthworms to pastures throughout the country.
Short-term and long-term investigations
Just as scientific investigations range in size, they also vary in the time it takes to run them. Some investigations run for a short time. Others can go for years – or even decades!
Dr Trish Fraser, a soil scientist with Plant & Food Research, has been involved with both short-term and long-term investigations. In one short-term investigation, Trish studied earthworm-burrowing behaviour using PVC cylinders 30 cm in diameter and 50 cm in length. She used soil from a nearby pasture to match the cylinders with field conditions. Trish added three different species of earthworms at rates commonly found in agricultural soils and sealed the cylinders with fine gauze to keep the earthworms in place and prevent others from entering. The cylinders were buried with the soil surfaces level with the surrounding soil and exposed to the weather. After 6 months, Trish removed the cylinders to study the macropores created by earthworm burrowing.
Trish tapped into a long-term pasture trial to aid her research into the effects of land management on the composition and size of earthworm populations. The Winchmore Irrigation Research Station began experimental fertiliser treatments in 1952, and the land has been continuously monitored ever since. Trish had access to Winchmore pastureland, a nearby wilderness area covered with native grasses and herbs and a site under intensive cultivation for 11 years. She excavated soil samples from all three sites to a depth of 25 cm and hand sorted the soil to collect the earthworms, which were then identified, counted and weighed. Trish’s research showed that earthworm numbers were lower under cropped land than either wilderness or improved pasture sites. This is primarily due to differences in organic matter input and rates of organic matter turnover. The cropped land had a lower supply of organic litter. The fertilised pastures had greater grass growth, more animal excreta and, consequently, more food for the earthworms.
Scientists often control conditions in order to focus on the effect of a single variable. This is often easier to do when conducting a short-term lab-based investigation. Field investigations using real-world conditions are then carried out to validate or verify lab results.
In this video, Dr Ravi Gooneratne describes how he uses controls in his earthworm/polluted soil experiments.