commentary

## Defending the Dependent Variable

A call to action

Fellow science educators, the dependent variable is under attack, and our students need our help to defend it! Why is the dependent variable under attack? Who is sounding the alarm? Let me answer these valid questions in reverse order. I am a high school science teacher who has just completed his second year of teaching. Prior to becoming a high school teacher, I was a university biology professor for 11 years, running an active research laboratory and teaching classes mainly in the biomedical sciences. As the years progressed, my love for teaching pulled me into secondary education.

With this inquisitive naivety on one hand (a secondary educator for two years) and rather practiced habit of thinking about the scientific method on the other hand (a practicing scientist for over a decade), I am asking for help in protecting our common friend, the dependent variable. Why is the dependent variable in peril? First, let’s clarify what it is and what it is not. Let’s then investigate the manners in which the dependent variable is at risk and how we may help students protect it. Finally, let’s take a look (through students’ perspectives) at how safeguarding the dependent variable will help science education thrive into the future.

### What is a dependent variable and what is it not?

Merriam-Webster defines the dependent variable as “a mathematical variable whose value is determined by that of one or more other variables in a function.” The dependent variable is the variable with which we measure changes that are caused by the independent variable (or interactions of several independent variables). The value of the dependent variable is not and cannot (by definition) be known before an experiment is conducted; it does not have a predetermined value. Conversely, the values of independent variables are known at the beginning of an experiment and are part of the experimental design.

The values of dependent variables are acquired by using our senses (seeing, hearing, smelling, feeling, or tasting), and we say that they are obtained empirically. However, the dependent variable is not always determined by our unaugmented senses. Depending upon the branch of science, the dependent variable is gathered using instrumentation (e.g., a microscope, a spectrophotometer, or a force meter), which serves as an extension of our natural senses. One may think of it as amplifying our natural senses or gathering information about our natural world below the detection level of our own senses.

The outcome(s) and value(s) of the dependent variable can only be known for the duration of time and within the parameters that they have been studied. The value of the dependent variable can be somewhat fickle and subject to naturally occurring fluctuations, and thus the proper acquisition of the dependent variable is beholden to experimental replication—especially in the biological sciences. If a dependent variable is not identified and measured in a given study, this does not mean that it does not exist. The obtained values of the dependent variable can be objectively recorded, but they are influenced by the manner in which an experiment is designed, what equipment is used, etc.

Once the values of the dependent variable are objectively obtained, these results must be connected to already-known findings, interpreted to reach a scientific conclusion, and shown how they interact with the world around us. Despite our best efforts, such interpretations are inherently subjective, and multiple views must be considered. For example, much scientific literature connects the burning of fossil fuels to climate change. Does that mean that all fossil fuel burning on our planet should be halted tomorrow? Even a strong climate advocate would likely acknowledge that this would likely lead to economic, food, security, and other problems. The dependent variable can tell us empirically about our world, but it alone cannot tell us how to interact with our world.

### Why does the dependent variable need defending?

What is threatening the dependent variable and why do students need help defending it? Our world is changing at an ever-increasing rate, and herein lie the threats. Students need help improving their ability to identify and understand the dependent variable. Let’s investigate some key points.

#### Infrequent practice using their own senses to interact with the natural world

Today’s students do not have as much practice directly using their own senses to gain information about the natural world compared with previous generations. This is not a criticism of today’s students, who have many impressive qualities; it is just an observation of the world they live in. Many children today find themselves bouncing from one structured activity to another, whereas children of yesteryear may have roamed the neighborhood as a pack exploring the natural world before dinner time. Unstructured interactions allow children to explore cause (independent variable) and effect (dependent variable) relationships while interacting with the natural world where the results are much more unpredictable, delayed, and varied. This is something that teachers need to keep on our collective radar.

For example, have you ever had a student in chemistry class indicate that a low concentration of hydrochloric acid yields no reaction with aluminum? Their observational skills have not been trained to detect subtle reactions or those that take more than a few minutes to occur. If you asked students in your biology class what roly-polies (pill bugs) residing underneath a rock will do when you pick up the rock, what will your students do? Will they go outside and check, or will they use a device to check YouTube? With an uneasy chuckle, I bet most of us will acknowledge that it is probably the latter. As the internal laughter dies down, let’s ask ourselves, “So what… What’s the harm?” Let’s delve into that question a bit.

Today’s students may be less reliant on drawing upon their own observations of the natural world and more reliant on a YouTube clip or what another individual says. This is antithetical to how the dependent variable is intended to function, as it may artificially skew observations and conclusions. A YouTube clip may show an individual picking up a rock and all the roly-polies underneath scurrying toward a nearby rock to reclaim their shade. But would this always happen? Is this behavior dependent upon the weather conditions of the day? Was it sunny or cloudy on the day this video was recorded? What season was it? Depending on the camera angle, the student watching the video may never know the answers to these questions, whereas the child exploring the natural world firsthand by themselves most certainly would have an appreciation for these important nuances.

Perhaps I, as the students’ teacher, could fill in these explanatory gaps; however, this would not be in my students’ best interest. We don’t want students to believe what an authority says about the experimental parameters or about what the value of the dependent variable “should” be; rather, we want students to believe what their senses indicate the value of the dependent variable is in reality.

Why? When these two values conflict (as they often do in science), we want students to believe their senses. This can sometimes be difficult and is a skill that students will need to practice. This is an enduring scientific practice that we want students to gain, and it demonstrates the importance of incorporating a level of freedom as students interact with the natural world in our science classrooms.

#### Limited use of scientific instrumentation to measure the dependent variable

Students could also practice using scientific instrumentation and equipment to augment their natural senses and measure the dependent variables they are attempting to observe. For example, one may consider the possibility that students don’t need to use a microscope anymore because lots of great microscopy images are already available online, but this thinking is problematic for two reasons. If a student views a microscope image taken by somebody else, the student is no longer gaining information directly from the natural world. It is no longer the student’s dependent variable; it is somebody else’s dependent variable that the student can see. We may momentarily think that this distinction does not matter because not everybody has access to scientific instrumentation, so the best that can be done is to have students view data acquired by others. This may sometimes be the case, but I would argue that a student must have as many experiences as possible using scientific instrumentation. It matters deeply, so let’s explore this point further.

In training students to accept a microscope image obtained by another, we are also inherently training them to trust the authority who has gathered this image. Is trusting another person inherently a bad thing? Of course not, but when observing a dependent variable, it is to be avoided if possible. When viewing data that others have obtained, there can often be selection bias—even if it is unintentional—in the field of view another person chooses when using a microscope. It can alter your objective reality, just as deciding where to focus your eyesight when driving can alter your objective reality.

Perhaps even more important, students should practice using scientific instrumentation as much as possible because they will not know what these instruments are capable of unless they use them directly. If a student lacks exposure to using scientific instrumentation, they will have a very limited understanding of the sensitivity of an instrument and how much the instrument is capable of augmenting one’s senses. This limits a student’s ability to ask scientifically plausible research questions. A student who has never viewed a sample with a microscope will never know the resolution it can give them of the microscopic world.

Additionally, using a scientific instrument firsthand enables a student to perceive directly what artifacts (mistakes) the instrument is prone to producing and how data can be processed by the instrument. Both of these factors are essential for a student to understand and to critically evaluate data acquired by others. It is imperative that students have time to use scientific instrumentation to augment their senses and view the dependent variable. Depriving them of this opportunity is akin to asking myopic individuals (such as myself) to observe the beautiful changing colors of autumn foliage without wearing their glasses.

#### Distracting electronic devices

Cell phones, tablets, and earbuds all interfere with observing transitory or subtle changes in the dependent variable. A simple metaphor is helpful here. A city-dwelling child may look up at the night sky amidst the bright city lights, be unable to see the stars, and be oblivious to the fact that they even exist. A child from the countryside may look at the same city night sky and acknowledge that the stars are not visible currently, but are likely still there because the child has seen stars before.

How many dependent variables are our students recording as zero, when in fact there is a value? It is more important than ever before that our students have time set aside in the classroom when the metaphorical city lights are turned off completely, so that they may fully observe and focus their attention on the given dependent variable of the moment. As educators, we need to consciously remind ourselves that having unnecessary electronics out of sight is essential to perception of the dependent variable and student learning in the science classroom.

#### Insufficient time for interdisciplinary science experiences

In a well-intentioned effort to cover all the topics that our students need to know in a given course, we may sacrifice interdisciplinary science experiences that teach valuable lessons about the fickle nature of the dependent variable in increasingly complex systems. Put more simply, if students in a physics course calculate the force of gravity by repeatedly dropping different rocks in a vacuum, my guess is that the variation on that gravity calculation would be pretty small. Chemistry students repeatedly calculating the reaction rate of a given chemical reaction may note a slightly higher level of variation. However, if we scale an experiment up to the biological level by investigating the effect of a newly synthesized chemical on the allergic response of certain types of aquatic life, some subjects may experience severe, life-threatening allergic responses; others might experience mild irritations; and many subjects may experience no symptoms at all.

These intrinsic alterations in variation of the dependent variable in different scientific fields is most noticeable when a child explores nature on their own. Since this likely occurs less frequently for today’s students, it is even more important to offer as much time as is feasible in today’s science classroom for interdisciplinary investigations that mimic informal explorations of the natural world.

#### How does defending the dependent variable help science education thrive into the future?

What do these threats to the dependent variable have in common? Whether they prevent students from actually measuring the dependent variable or understanding what the dependent variable is and what it is not, we can generalize and say that these threats may prevent our students from knowing the dependent variable. This brings us back to our original question: Why is it important that we defend the dependent variable? The answer is that the more distant our students become from the dependent variable, the more distant they will become from the scientific method. They will have difficulty recognizing the proper execution of the scientific method, in their own work or in the work of others.

In other words, the values of independent variables are intentionally chosen by students prior to commencing an experiment (with a nod to prior experiences and research playing a role), and they may not be as adversely affected by inattention during the actual running of the experiment. The values of the dependent variable, however, are chosen by nature, in real time, during the course of the experiment. Our students must be undistracted and trained to properly document the dependent variable at the right moment. Students select what categories to measure as dependent variables beforehand; however, they do not know (and cannot select) the actual quantitative or qualitative response of the dependent variable before the experiment. Their attention must be focused at that instant in time. If it is missed, it cannot be recovered.

What does this mean for the science classroom? Today’s students will benefit from authentic, repeatable, interdisciplinary experimentation in the science classroom. Canned experiments (where the results are already known) should be avoided when possible. Rather, novel investigations should be encouraged, where students are truly interacting with the natural world to ask and answer a question that has not yet been fully explored by others.

#### In practice: A weeklong learning segment

Students can learn how to use a new instrument or piece of equipment (e.g., voltammeter, calorimeter, or gel electrophoresis) to measure a given dependent variable. Then to provide both structure and perspective, they can show how to independently produce a positive control and a negative control using this piece of equipment, but they should be allowed to select the experimental group that is being studied.

The positive control and negative controls should be time tested and true, because that is what they are in actuality. Students should have time to practice these controls to ensure that they can repeat them with sufficiently low levels of variation—this in itself is a worthwhile exercise, as it trains their observation toolkit to detect nuanced variation in the dependent variable both within a group and between groups.

The students can then select their own independent variable and related experimental group. It should be one that interests them, relates to their life, and one that has not been measured before by others. In this manner, they have the freedom to engage in a novel, authentic research experience—with positive and negative controls for comparison—so that they may draw conclusions from their experiment. Additionally, if their experimental group should yield uninterpretable results, they still have the baseline experiment that the positive and negative control inherently yield.

During the experiment, electronic devices should be put away, unless they are being used to augment students’ senses and/or record the dependent variable. When I have tried different iterations of this learning segment in class, student engagement has been invariably (pun intended) high. This of course is not the only approach that can be used, but it is an option to explore.

### Conclusion

In an era when science touches almost every aspect of our lives, it is essential that the scientific method remain a self-correcting method that students can use to learn about the natural world. Having citizens who know the scientific method is essential to the proper continuation and evaluation of hypothesis-driven scientific research in today’s rapidly evolving world. This begins with our successful safeguard of the dependent variable in today’s science classroom. Students will come to know the dependent variable through freely engaging in authentic, repeatable, interdisciplinary experimentation in our science classroom.

The importance of the dependent variable is recognized by the three-dimensional learning of the Next Generation Science Standards (NGSS). It is not a coincidence that six of the eight NGSS science and engineering practices rely directly on a student’s ability to understand and recognize the dependent variable. Protecting the dependent variable is arguably the most important measure teachers can take to protect students’ ability to execute and evaluate the scientific method itself.

Eric Michael Bratsolias Brown (brownsciencegroup@gmail.com) is a science teacher at Adlai E. Stevenson High School, Lincolnshire, IL.

Pedagogy Teaching Strategies High School