To investigate causal linkages, experiments are utilized. While conducting experiments, one or more independent variables are changed, and their influence over one or more dependent variables is observed.
The phrase “experimental design” refers to developing a set of tools for systematically evaluating a hypothesis. A solid understanding of the system under research is required for a good experimental design.
You must follow these five steps to creating an effective experimental design:
You must also pick a representative sample and regulate any confounding variables that may impact your outcomes to draw accurate conclusions.
1. Defining variables Begin by formulating a precise research question. Then, we’ll look at two different research questions, one from public health and the other from ecology:
Question 1: What is the relationship between smartphone use and sleep patterns?
You’re curious to study the effect of smartphone use before bed on sleeping patterns. So you explicitly inquire as to how many minutes a person spends on their smartphone before going to bed and how it influences their sleep quality.
Questions 2: Impact of temperature on soil respiration
You’re curious to know more about the effect of temperature on soil respiration. You specifically inquire about the effect of higher ambient temperature near the soil surface on the concentration of co2 respired by the earth.
You must specify the essential variables and make inferences about how they are connected to turn your research objective into an experimental hypothesis.
Begin by writing down all of the independent and dependent variables.
Research objective/question |
Independent variable |
Dependent variable |
Smartphone use and sleep patterns |
Screen time before sleep |
The number of hours of sleep. |
Impact of temperature on soil respiration |
Ambient temperatures above the soil. |
The concentration of carbon dioxide respired from the soil. |
Now you must evaluate any potential extraneous or confounding factors and minimize these variables in your experiment.
|
Extraneous or confounding Variables |
How to minimize |
Smartphone use and sleep patterns |
Individual sleep patterns are subject to natural variations. |
Statistical Control: Rather than measuring the average quantity of sleep per treatment group, assess the average difference between sleep hours; with and without smartphone usage before going to bed. |
Impact of temperature on soil respiration |
The amount of moisture in the soil impacts respiration and moisture levels might drop as the temperature rises. |
Experimental Control: To ensure that soil moisture is uniform throughout all treatment plots, check soil moisture and provide water as needed. |
Finally, you may create a flowchart using these variables. Again, incorporate signs to reflect the predicted direction of the connections and use pointers to show the possible links between variables.
2. Write your hypothesis
You should be able to construct a particular, testable hypothesis that addresses your research question provided that you have a sound theoretical knowledge of the system you’re examining.
|
H0 (Null Hypothesis) |
H1 (Alternate Hypothesis) |
Smartphone use and sleep patterns |
The amount of time spent on a smartphone before going to bed has no bearing on the quantity of sleep a person obtains. |
Increased screen time before bedtime results in less sleep |
Impact of temperature on soil respiration |
Soil respiration is unrelated to air temperature. |
Increasing soil respiration is a result of increased air temperature. |
The following steps will show you how to create a controlled experimental design. But, first, you must be able to do the following in a controlled study:
If your experimental design does not meet these requirements, you can utilize alternative types of research to address your research question.
3. Designing experimental treatments
The experiment’s external validity – that is, the amount to which the results may be extended and applied to the larger world – is influenced by how you manipulate your independent variable.
You need first to determine how much you want to modify your independent variable.
Experiment with soil warming
You can opt to raise the temperature of the air:
Next, you may need to decide how finely your independent variable should be varied. Again, your experimental system may make this decision for you, but it is up to you, and how much you can deduct from your data will be affected by it.
Experiment with cell phones
You have the option of treating phone use as follows:
4. Assigning subjects to treatment groups
For accurate and trustworthy findings, you must apply your experimental treatments to your test participants in a certain way.
To begin, think about the magnitude of the study: how many people will be involved in the experiment? Generally, the more individuals you enrol, the better the statistical power of your experiment, which influences how confident you may be with your findings.
Then you must allocate your subjects to treatment groups at random. Each group receives treatments at a different intensity.
Include a control group that does not get any therapy. The control group describes what would have resulted if your test participants had not been subjected to the experiment.
When it comes to dividing your subjects into groups, you have two options:
Randomization
A study can be entirely randomized or randomized within blocks (also known as strata):
Every subject is allocated to a treatment group randomly in a completely randomized design.
A randomized block design which is also known as a stratified random design groups subjects based on a shared trait before randomly assigning them to treatments inside those groups.
|
Completely randomized design |
Randomized block design |
Smartphone use and sleep patterns |
A random number generator is used to assign a degree of phone use to each subject. |
Subjects are divided into groups based on their seniority, and then smartphone use treatments are allocated at random among these groups. |
Impact of temperature on soil respiration |
By utilizing a number generator to produce map coordinates inside the research area, warming treatments are allocated to soil patches randomly. |
Soils are divided into categories based on average precipitation, and treatment areas are randomly distributed among these groups. |
Researchers construct partially random or even non-random experimental designs when randomization isn’t realistic or moral. A quasi-experimental design is an experimental design in which treatments are not allocated at random.
The difference between the “Between-subjects” and “within-subjects” approach
Individuals receive just one of the possible levels of an experimental treatment in a between-subjects design. It is also known as an independent measures design.
You may also use matched pairs in your between-subjects design in medical or social studies to ensure that each treatment group has the same number of test subjects in the same percentages.
Every subject gets each of the experimental treatments one after the other in a within-subjects design, and their responses to each treatment are assessed.
Within-subjects or repeated measurements relate to an experimental design in which an impact occurs over time, and individual responses are assessed to track this influence.
Within-subject experimental designs frequently involve counterbalancing (randomizing or reversing the sequence of treatments across subjects) to guarantee that the sequence of treatment administration does not impact the experiment’s outcomes.
|
Independent Measures (Between-subjects experimental design) |
Repeated Measures (Within-subjects experimental design) |
Smartphone use and sleep patterns |
Subjects are allocated a degree of smartphone usage (none, low, or high) at the start of the trial and must maintain that level throughout the investigation. |
Throughout the study, subjects are assigned to three degrees of phone usage: zero, low, and high, with the sequence in which they receive randomized treatments. |
Impact of temperature on soil respiration |
Warming treatments are randomly allocated to soil plots, and the soils are maintained at this temperature for the duration of the study. |
Each plot receives each heating treatment (1, 3, 5, 8, and 10 degrees Celsius above room temperature) in the same order throughout the study. The order in which they get those treatments is randomly chosen. |
5. Measuring your dependent variable
The final step of your experimental design is selecting how you will gather data on the results of your dependent variable. Again, you must strive for consistent and precise measurements with slight bias or inaccuracy.
Variables like temperature, for example, maybe measured reliably using scientific tools. However, others would require operationalization to become quantifiable data.
Smartphone use and sleep patterns example
You might assess your dependent variable in your experiment about smartphone use and sleep in one of two methods:
The types of statistical analysis you might perform on your data are also influenced by how accurately you measure your dependant variable.
Experiments are always dependent on the context, and an effective experimental design will consider all of your study system’s specific factors to create appropriate and reliable data to your research question.
Experimental design is the process of planning a collection of approaches to investigate a relationship between variables.
Independent and dependent variables are considered as action and reaction: an independent variable is the action variable, while a dependent variable is a variable that is the consequence.
A control group is the group of subjects that receives no therapy. On the other hand, a treatment group receives the treatment whose effects researchers seek to explore. Apart from this difference, both should be identical in every other way.
Both the apparent cause and the ostensible outcome of the investigation are tied to a confounding variable. Thus, it can be difficult to distinguish between the actual influence of the independent variable apart from the effect of the confounding variable.
Therefore, it is crucial to recognize potential confounding variables and figure out how to reduce their impact on your experimental design.
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