Variables in Science Experiments What makes an experiment “fair”?
Science experiments use… Independent Variable: the one and only factor that is changed in an experiment. Dependent Variable: the factor which is measured/observed in the experiment. Responds to changes in the independent variable. Controlled variables: all the factors that stay the same in an experiment
A birdy example… Imagine you want to see what color of bird feeders your local birds preferred. Red? Blue? Green?
Variables Independent Variable: color of the feeders Dependent Variable: amount of seed eaten Controlled: everything else that is kept the same, for example: – the location of the feeders – the kind of feeder used – putting the feeders out at the same time
Our Experimental Design Controlled variables Location of feeders Kind of seed Type of feeder Independent Variable Red Blue Dependent Variable Amount of Seed Amount of Eaten Seed Eaten Amount of Seed Eaten Green
If everything except the independent variable is held constant, we can say: The experiment is FAIR. (ONLY the independent variable can change!)
Is Sam’s experiment fair? YES? NO?
Why is it important to change only 1 thing at a time?
If you don’t… then you won’t know what is causing your results. Independent Variable
How does diet affect a fish’s ability to swim through a maze? Patrick thinks fish that each microwaved food are smarter than fish that do not. Patrick times the fish going through a maze before and after eating. 10 fish get microwaved food. 10 fish get non-microwaved food.
Variables Independent: Microwaved food or not Dependent: time it takes to get through the maze Controlled: Fish species, maze, amount of food, type of food.
How does a special juice affect worker productivity? Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1, 587 stacks, Group B made 2, 113 stacks.
Smither’s experiment Independent variable: Juice or not Dependent variable: Number of stacks of papers Controlled variables: 50 workers were in each group. They shared the same task Uncontrolled: The group that did not consume juice should have consumed the same amount of water.
How does diet affect the length and complexity of starling bird songs?
Contaminated versus Noncontminated food source. Starlings that ate a controlled diet were compared to those that ate earthworms from a sewage treatment plant. The starlings that ate earthworms contaminated with estrogen sang five times as long as the starlings on a controlled diet. They also sang more complex songs.
Starling experiment Independent: Diet contaminated or not. Dependent: Length and complexity of songs. Controlled: Starlings Uncontrolled: Age/gender of bird.
How does brain size compare in taxi versus bus drivers? The taxi drivers drove different routes every day. The bus drivers drove the same route every day. Discovery: Taxi drivers has a larger spatial memory (the part of your brain that helps you navigate) than bus drivers.
Variables Independent variable: Taxi versus Bus Driver Dependent: Spatial memory Controlled: Same city Uncontrolled: Intelligence, Years of driving experience.
Do marigolds planted in moon rocks grow best with or without microbes? Two groups of marigolds were planted in crushed rock that is very similar to rocks found on the moon. Group 1: Microbes were added to the soil. Group 2: No microbes were added Discovery: The marigolds with microbes added to the soil grew best!
Independent: Microbes in soil or not Dependent: Plant height Controlled: same amount of soil and water Uncontrolled: health of the plant
What do you think? Terry loves birds and wants to see as many as she can in her yard. She wants to know whether she is wasting money buying an expensive mixed seed, when a cheaper brand just arrived at her local store. She wonders… will the expensive seed attract more birds to her back yard? How would you advise her to find out if the expensive seed is better?
Terry’s Experimental Design Independent Variable ? Dependent Variable ? Constants ?
Terry’s Experimental Design Independent Variable Kind of seed: Expensive Cheap Dependent Variable Number (and perhaps kinds) of birds that visit Constants Location of feeders Type of feeder Way she measures the amount of seed eaten and the way she counts birds $
What experiments are you planning? What are your variables? How will you keep your experiment fair?