Experimental Design

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Experimental Design
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Division B Champion Daniel Wright Junior High School
Division C Champion Seven Lakes High School

Experimental Design has been an event in Science Olympiad in both divisions for many years. In this event, you will be given several materials and asked to perform an experiment on a certain science topic. You will then be required to write-up the experiment in the "lab write-up," which will be used to score you.

Contents

Key Points to Include in a Lab Write-up

Statement of Problem

This is a question posed that will be explored in the experiment. It should not be a simple yes or no question. Try to use the key words, "how" or "why". Remember "KISS", or "Keep It Simple, Stupid!" -and always remember to be neat! One of the formats that can be used for almost any experiment is "How does (Independent Variable) affect (Dependent Variable)?"

Hypothesis

The hypothesis is a guess as to the result of your experiment, relating to the statement of the problem. It should express how the changes to the independent variable will affect the dependent variable. A rationale for the hypothesis should be included. Make sure you have the correct DV (dependent variable) and IV (independent variable). If you have misidentified these two, it's likely you won't get very much else right. "We predict" is a good starter, but tends not to yield full points. It is best to not include this, but instead act as though you know it is completely true.

Variables

There are three different kinds of variables you should define in your lab writeup. The three different kinds of variables could be, for example, in a lab which uses different masses, a nine gram weight, a twelve gram weight, and a fifteen gram weight.

Controlled Variables (CV)

Controlled variables are factors which could effect the dependent variable, but are kept constant throughout the experiment. Several controlled variables should be listed (usually four is a good amount). For example, if the experiment is testing to see how fast a parachute falls with different mass, a constant variable could be "Height at which parachute is dropped (in meters)".

Independent Variable (IV)

This is the variable that is changed to examine its effect on the dependent variable. There should only be one IV, which should be listed with units.

Dependent Variable (DV)

The dependent variable is what is affected by the independent variable. It should be defined in units. Using the same previously given experiment, this would be "Time it takes for parachute to fall (in seconds)."

Control or "Standard of Comparison"

A rationale for the control should be included. The SOC is basically the object that is the "normal" one, the one that hasn't been changed at all. For example, if you were doing an experiment on how long a can spins v.s. how many holes it has in it, the SOC would be the can with no holes in it. Changing your DV to zero, or using the highest or lowest possible numeric value makes a good SOC.

Materials

When you list out your materials, be sure to be extremely specific. It is a good idea to write down brand names or companies next to the material. After all, different companies make different versions of the same thing. When you list your independent variable (say you are testing using three different weight rocks), write "Rocks (light, medium, heavy). If you aren't sure whether or not to list the materials you used to measure (meter sticks, time pieces, etc.), ask the event supervisor. Some competitions want you to list the measuring devices, while others may take off points for it.

Procedure

List the steps in your experiment clearly. Be sure to include diagrams of how your experiment was performed. To cut time, "Repeat steps X to Y" can be used, but make sure it makes sense. You can check yourself by imagining if you could show any random person the procedure, would they be able to follow it clearly? Always have three trials for each step. Without this, a single data point may be an outlier- or it may be a real data point and you would never know. Remember to be specific all the time. The last thing on every procedure list should be "Clean up your workspace"- and be sure to do so!

Qualitative Observations

List four qualitative observations. Qualitative observations are those that describe an observation of non-numerical data- i.e. the parachute seemed to open up more with a heavier mass. List anything that you see that might have been a problem in the procedures as well ("Parachute did not open on trial three"). Do not list anything that has to do with the dependent variable. Saying "The parachute with the heaviest weight fell the fastest" would be in violation of that rule, thus not earning points.

Quantitative Data

One way to organize the data is to make two tables. For the first, make a table of four rows and four columns. The first column should consist of, from top to bottom, a blank box, IV 1, IV 2, and IV 3. The second column should be labeled "Trial 1", and following boxes filled accordingly to the data. The next two columns follow the same layout as the Trial 1 box, but with Trials 2 and 3. Title the graph as seen fit for the data. Next to that table, draw a one column, four row condensed table (to the right). Name it "Average" (or AVG for short), and average the data for each IV. Put arrows from the second row of the first table to the second row of the condensed table, and so forth. Give a sample calculation for the average ((Trial 1+Trial 2+Trial 3)/3), located below the table or on one of the arrows.

Graph

A standard bar, line, or scatter-plot graph works almost universally at any competition level. Even so, always be sure to use the correct type for your data. Always remember to:

  1. Label your axis (x+y)
  2. Title the graph
  3. Use the DV as the y value and IV as the x value
  4. Title the individual axis (For example, left of the y axis you would write, "Time taken for parachute to fall (seconds)")
  5. Connect the data points or draw a line of best fit
  6. Only include the averages of the data for each IV

Statistics

Take the common statistics - mean, mode, range, median. Also include any other relevant statistics and show work. The best idea is to put all statistics in a neat table.

Once your common statistics are done, make sure to do some more. Standard deviation is a very good statistic to include. The equation for calculating standard deviation is: \sigma = \sqrt{avg((value - mean)^{2})}. For a better visual equation and an explanation of what standard deviation is (which you will need to know to explain the statistic), see Standard Deviation. Actually doing trials is necessary, as a standard deviation of a sample size of 1 is clearly stupid. A key point that is easy to miss is the deviation has to be squared. If you don't, your result will always be 0, and though this may look pretty, it should be obvious that your data does not have a standard deviation of 0.

Your table of data should be neat- a ruler helps a lot. Be sure to keep writing your units. Also be sure to keep your significant figures consistent and logical. You do not want to have a number down to three decimals when your ruler can only accurately measure to one decimal. See Significant Figures for additional info about significant figures.

Graph your data. Make the graph neat, legible. Use a legend if need be. Label the axes (with units) and make a title for the graph (including units here as well is a good idea; for example, "Time in takes a parachute to fall, in seconds, vs the weight, in grams".

In Division C, you will be expected to do more with the data. One essential aspect of the graph will be to create a regression, or line of best fit. Basically, since you're not really expected to have all the tools necessary, you won't be expected to make anything but a linear regression. If you can have your calculator create an accurate logarithmic regression. more power to you, but make sure to allot the appropriate amount of time for this section. The best fit line of dubious accuracy is made by drawing a straight line with a ruler that you think seems to go as close to all the points on the graph. Once you do, find the y-intercept, and calculate the slope. Make sure to consider which outliers are significant, and which are experimental errors. If you make these kinds of judgment calls, make sure to point it out and explain it in the Analysis section.

Also, make sure you always have the same units through-out the experiment, if you are using milliseconds in the data table continue using milliseconds for everything else, DO NOT change to seconds or any other units.

Analysis

Look at the data and draw some reasonable conclusions about the experiment. There should be trends; point them out and explain them. Discuss your statistics and again, explain them. Guesses are okay, even if they're wrong; they show your thought process. If you have any outliers or random "bad" data points, don't ignore them - again, write about them. Was there anything you did wrong that time, or was it just a fluke?

Possible Sources of Experimental Error

Look for all the things wrong with your experimental setup. How might they have caused inaccuracies in your data? This is extremely useful, because it can redeem mistakes made earlier in the event by showing that you are aware of them. Sometimes points can even be regained. Try to stay away from human errors and try to focus on experimental sources of errors like you can say things that have to do with temperature. The container of your object may have insulated it. Say any possible thing that could change the outcome of the experiment.

Also, this section can be written before any data is actually collected, and just added to if there are glaring errors in data collection that you didn't predict. If you're not sure how the experiment is going to turn out, this is a good thing to write first.

Conclusion

Answer your Statement of the Problem. Evaluate your hypothesis. Was it correct? How would you improve the experiment's procedure, if you were given another chance? Would you run a completely different experiment, with a more accurate or visible trend? What problems did you have in the experiment, and how would you fix them if the experiment was done again?

Applications and Recommendations for Further Experimentation

Consider your experiment and how it may apply to a real-life situation. For instance, the aforementioned parachute experiment could help skydivers know when to unleash their parachute. Then, think of related experiments that could shed more light on the same or a similar topic. How could your results be practically applied? How could the results of another experiment combined with the results of your experiment help? Where is it useful in real life? This section can also be written without any knowledge of how the experiment will turn out, and so it can also be written before data has been collected.

Common Strategies

Knowing the scoring rubric is the key to success in Experimental Design. The rubricis a set of guidelines used for scoring experiments. When experimenters are aware of what is expected in each section, it becomes much easier to work efficiently.

At the start of the event, start by brainstorming possible experiments. Expect to get a handful of seemingly random items to test with, along with the possibility of a topic or prompt to design the experiment around. If each team member is familiar with general scientific concepts, designing an experiment should not be too difficult. Focus on execution and write-up, not on preparation.

Keep your experiment simple. Too many variables can mean a lot of writing. Consider an example experience from one regional tournament. 3 balls (different colors), 2 rubber bands, a foot of masking tape, a metric stick, and a mini catapult were given. Naturally, one would want to experiment with the fanciest item given (catapult, in this case), but there would be so many variables to consider. Instead, performing a dropping experiment on how a rubber band affects the time it takes for a ball to drop. This is much simpler and, in this scenario, an idea that definitely paid off. Teams that used the catapult had balls flying everywhere throughout the event, and team members had to run around searching for them; wasting time. On the other hand, teams that utilized the other equipment achieved third out of thirty teams. Moral of the story is, ignore the urge to fiddle around with the complex stuff. Keep it simple- experiments will be simpler to write and test, saving time.

However, be sure to have enough trials. Having 3-5 trials for each variable ensures that data is sound and statistics have merit. This way if there is a possibility of strange data (one test being too high/low/fast/slow) there is the "experimental errors" section to comment on that. Only having 1-3 trials means there may not be enough data to show that a data point is strange, because there are not enough points to compare it to.

Know who is doing each section before the competition. All 3 people don't need to be doing the lab; only 1 or 2 people should be experimenting. Don't spend the whole time doing the lab either, 15-20 minutes should be plenty to get a significant amount of data for an experiment. There are many ways to divvy up the work on this event. Find something that works, each group is different.

If the experiment goes horribly wrong and all the data is skewed, focus on the report as much as possible. Make sure to explain why the experiment was bad and where it went wrong. This is where "Possible Experimental Errors" really counts-- be sure to write and explain every error which caused the experiment to go wrong. Having a bad experiment but a very good report can, in some cases, cancel out the fact that the experiment didn't work.

Just like any other event, practice! Have a fellow teammate or coach gather materials and come up with a possible topic. Spend 50 minutes and come up with, test, and write up a lab report. Have the coach/teammate then grade the lab based on the rubric. This gives great insight into time usage and where improvements need to be made.

How to do your best

In Experimental Design, you should always keep your experiment reasonable. Here are some tips for how to do your best:

  1. Come prepared. You should come to the competition equipped with several different writing utensils, a ruler, a stopwatch and a non-programmable calculator.
  2. Study the rubric. You might be able to use it, but just to be safe always look over the rubric before the competition.
  3. Be neat. If the judges can't read your experiment, they are not going to take it. Find someone in your three people group who has neat handwriting.
  4. Think outside of the box. Don't do what everybody else will. The judges need to see that you are uniquely intelligent.
  5. Be efficient. Sometimes, "slow and steady wins the race" doesn't always apply.
  6. Be precise, especially when labeling your list of materials. You can never be too specific in this event!
  7. KISS! Keep it simple, stupid!

Practice trials

Links

Experimental Design National Page (Div. C)

The rubric for Experimental Design The rubric rarely varies from year to year

See Also