Catalyst

Errors in Science

Two types of errors in science: human error and experimental error

Human Error

A human error is an error made by the scientistThe most likely error in an experiment is human

error. Unfortunately, we are not perfect A human error makes the conclusion not valid.

Types of human errors:• Biases• Not following the procedures of an experiment (for

example, missing or adding a step)• Making an error in measurement or calculation• Assuming a cause and effect relationship without data• Not having a controlled experiment

Biases

Biases are wishes or expectations that will lead to a certain conclusion

Can be intentional or unintentional

Some sources of biases: Trying to persuade someone else Relying on incomplete information Past experiences are influencing you

Biases in Action

Ms. P thinks that Penn State is the best university in the nation! She conducts an experiment to see which college campus is the cleanest campus and she concludes that Penn State does.

Biases:

•Need to make careful observations •Example: Testing a drug, must measure the symptoms, not whether the patients say they feel better

Procedure

You must follow the procedures of an experiment exactly.

If you make an error in the procedure, you must completely re-do the experiment!

Making an Error in Measurement or Calculation

Most frequent error calculating change

When calculating a change in an experiment, you must always do the final value minus the initial value

Change =final - initial

Examples of Not Calculating a Change Correctly

After placing the rock in the graduated cylinder, Ms. Baggs said the volume of the rock was 30 ml.

Remember – the volume of the rock is equal to the change in volume (final volume – starting volume)

This is an example of human error because he made the mistake – if she was perfect, she would not have made this mistake!

Another Example

A farmer is trying to see what type of fertilizer has the largest change in height growth on his wheat.

He measures the height of the wheat after each fertilizer has been administered.

Remember, change = final – starting.

What does the farmer know?

Final - ?????

How is he suppose to know how much it grew? He only know its final height. What if one started out much taller?

Want kind of error is this?Example 1Professor Messer is trying to measure the length of a piece of wood:Discuss what he is doing wrong.

How many mistakes can you find?

Human error

1. Measuring from 100 end2. 95.4 is the wrong number 3. ‘mm’ is wrong unit (cm)4. Hand-held object, wobbling5. Gap between object & the rule6. End of object not at the end of the rule

Answers:

Cause and Effect

In order to assume a cause and effect relationship has occurred, there has to actually be proof of a cause and effect!!!

You need to back, back, back that up with evidence. You must have experimental data that proves there is a cause an effect relationship between your independent and dependent variable, before assuming there is one.

Annie could hear the music playing over the loud speaker in the mall. She and her mother were shopping for a present for her father. Annie could see a big line in the center of the mall. She wondered what all the people were waiting for. She then heard a jolly "HO! HO! HO!" from the center of the crowd and she quickly realized what the people were waiting on. As Annie and her mother walked through the mall, she noticed that the store windows were decorated with green, white, and red decorations.

It actually was not Santa…

It was the Allstate guy promoting insurance at Christmas time!!!!

Controlled Experiments

You also need to make sure your experiment is controlled.

A controlled experiment has: ONE independent variable and ONE dependent

variable Control group and experimental group All other variables are controlled (control variables)

Control Variables

For example, if Mary wanted to see the effect of saltwater on plant growth, she needs to use the same type of plant, give it the same amount of sunlight, the same amount of water, etc. She also needs to compare it to a plant with regular water in order to make a conclusion.

Example: Juan wanted to see how the amount of food given to a dog affects its energy level. He has two dogs at home: a small poodle and a big Lab. Can he use these two dogs and only these two dogs in his experiment? Why or why not?

Think, Pair, Share!

1. I will show an experiment and ask you a question about it.

2. You will have 10 seconds to think about the answer by yourself. This step should be completed silently.

3. Then you and your partner will come share your ideas.

4. 1 group will be cold called to share their answer.

Two birds are fed different types of bird seed to determine which type causes the bird to gain more weight. Which of the following would be an experimental error? A. The birds are different species. B. The birds are allowed to eat all the seed

they wanted. C. The birds are exposed to different amounts

of light and heat. D. All of the above.

Example #1

Two birds are fed different types of bird seed to determine which type causes the bird to gain more weight. Which of the following would be an experimental error?

We can only have ONE independent variable, which means we can only change one thing! The ONLY thing we should be changing is the type of seed!

A. The birds are different species. they have to be the same species

B. The birds are allowed to eat all the seed they wanted. they need to eat the same amount of seed!!

C. The birds are exposed to different amounts of light and heat. the need to be exposed to the same amount of light!

D. All of the above.

Example #2Jonquil decides to test the effect of light exposure on the growth rate of a particular species of plant. He sets up his experiment as shown above and measures the height of the plants each day for a month. He makes sure to water the plants daily, each with the same amount of water. After collecting and analyzing the data, he notices that there is little variation in the height of the plants. Even though the plants received different amounts of light from each lamp, they are all the same height. Jonquil is surprised by these results. What should he have done differently?

A. Measured the plants more often

B. Used the same amount of light C. Moved the plants away from

the window

Example #3

Ms. Vekilov was raving about how well she could bake. Ms. P got tired of listening to her and decided to have a bake off to settle Ms. Vekilov once and for all. Both teachers bakes they’re best desserts and handed them out in class. As Ms. Vekilov handed hers out she talked about how delicious they were to each student. What kind of error is taking place?

Experimental Error

Not always a mistakeDifference between the “true” measurement

and what you measureOccurs because no one is perfect and

because tools are not perfectExample: Measuring a seed length:

One scholar measures 6 mm, another scholar measures 7 mm. Actual is 6.5 mm

Experimental Error

•Too much = NOT valid conclusion.

•Limit error:•repeat measurements and average•Have several trials in your experiment

Summary

Any human error = invalid experiment

Any experimental error = could still be a valid experiment

Error Stations

Work with a group of 4

You will be given 4 minutes at each station to read the experiment and answer the questions