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How many times should I do my science experiment?

Definitely more than once!

 

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by Lani Yamafuji in how to
How many times should I do my science experiment?

 

Hi Edgar! Thanks for your science experiment question.

“I did a project about onions and how well they grow with different amounts of water; one and a half cups of water, one cup of water, and a quarter cup of water. The one cup of water did not grow. Meanwhile the other amounts of water grew. Why is this?”

Let’s assume that since you changed the amount of water in each test, you kept all the other variables the same. This means you kept the containers, the soil, the light, the temperature, the time, the type of onion, and everything else in your experiment the same.

Why did the onion in one cup of water not grow? Well, there could be many reasons. Maybe that onion was smaller, or diseased inside, or weak, or just a very slow grower.

Science Experiment Trials

Edgar, this is a great example of a project showing just how important it is to do multiple trials – which means, you should do your project more than once to see if the results are really accurate.

My son once did a project about rolling dice. He wanted to find out if, when rolling a 6-sided die, the numbers 1 through 6 came up the same number of times. What if he rolled it once and the number 3 came up? Could he assume that the number 3 always came up? Of course not! When he rolled it twice, could he predict that the number 3 would come up again. Nope. He decided that he needed to roll that die 1,000 times, to make sure his results were accurate. (He avoided nasty hand cramps by rolling the die about 10 times a day over a few months).

Repeat your science experiment to make sure the results are accurate

How Many Times is Enough?

Do I think you need to plant 1,000 onions to make sure your results are true? No! And this is a tough one – different projects need to be repeated a different number of times.

How are you supposed to know how many trials to do for your experiment?

I would say, doing a plant growing project 4 times (yes, repeating the exact same project 4 times) and coming up with the same results would “prove” that this experiment was accurate. If the results are not the same, you should try and figure out why. Three out of 4 times with the same result, still pretty good.

If you were doing a project using people, then using a classroom sized amount of people is a good bet – 20 or so people. For example, if you did an experiment timing how fast corn travels through a person, I wouldn’t just use one person. People have different digestive system speeds. (Yes, I’ve seen this project done before on just 4 people. Ok project. It would have been better with more people.)

Do I have to repeat my experiment one after another?

No. I would suggest doing all the experimenting at the same time to get it done faster.

So, Edgar, if you still have time, try repeating your science experiment at least one more time. Three more times, if you want to be really sure about your results.

If I am totally off base, and you actually did your project many times, and all of the onions in 1 cup of water didn’t grow while the others in 1 1/2 cup and 1/4 cup grew, then you have something very interesting going on.

It is important to look at your results and see if something doesn’t make sense. If you suspect something just doesn’t add up, then you should try the experiment again.

Good luck!

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GET YOUR FREE SCIENCE FAIR CHEAT SHEET!

Learn the 3 Secrets to Winning from a science fair judge, teacher, and mom. It could be life changing. Make this science fair the best ever!

it's 100% free!
Only for K-8th Grade Winners!