Science Assessment ~ Topics ~ Control of Variables ~ Item CV014003 ~ Student Performance

A farmer thinks that type of soil and amount of water affect the growth of his carrot plants, and he wants to find out if he is right.

The farmer first tests if the type of soil affects the growth of the carrot plants. He uses three different types of soil, and he places 10 carrot plants in each type of soil. He uses the same amount of water for all the plants.

Why is it important to use the same amount of water for all the plants?

By using the same amount of water, the farmer can learn about both the effect of the amount of water and the effect of the type of soil.
By using the same amount of water, the farmer can learn about the effect of the amount of water.
If he does not use the same amount of water, the farmer cannot learn about the effect of the type of soil.
It is NOT important to use the same amount of water because the farmer is not testing the effect of the amount of water.

Distribution of responses
Answer Choice		Overall	Grades		Gender		Primary Language
		n = 2683	6–8 n = 1510	9–12 n = 1159	Male n = 1322	Female n = 1337	English n = 2261	Other n = 379
A.	By using the same amount of water, the farmer can learn about both the effect of the amount of water and the effect of the type of soil.	23%	26%	19%	24%	23%	22%	35%
B.	By using the same amount of water, the farmer can learn about the effect of the amount of water.	13%	16%	9%	15%	11%	12%	18%
C.	If he does not use the same amount of water, the farmer cannot learn about the effect of the type of soil.	59%	51%	69%	56%	62%	62%	42%
D.	It is NOT important to use the same amount of water because the farmer is not testing the effect of the amount of water.	5%	6%	3%	5%	5%	5%	6%

Science Assessment

Item CV014003: To find out if type of soil affects the growth of carrot plants, it is important that all of the plants get the same amount of water because if they didn't, it wouldn't be possible to tell which soil type was better.