Topics-+Control+Of+Variables

Topic: Control of Variables
Below is a list of key ideas related to Control of Variables. For each key idea, you will find a list of sub-ideas, a list of items, results from our field testing, and a list of student misconceptions. After clicking on a tab, click on it again to close the tab. ==== If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables. -and- Item Type A1: Given an idea to be tested (hypothesis) and an experimental setup, explain why certain variables are (or should be) kept constant. ==== These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below. > //Students are expected to know that:// //Boundaries//: > This is an item type. There are no sub-ideas.
 * [|Sub-Ideas]
 * [|Items & Student Performance]
 * [|Misconceptions]
 * If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables.
 * 1) By changing a single variable at a time and holding all other relevant variables constant it is possible to determine whether that single variable is correlated with the outcome or not.
 * 2) When varying more than one variable at a time it is not possible to determine the correlation between either variable and the outcome of an experiment.
 * 3) The reason for controlling a particular variable (holding it constant) in an experiment is because it may have an effect on what is being tested.
 * 4) A variable is an entity that may assume different values, either quantitative or qualitative, not a particular value of a variable. For example, when “types of liquid” is defined as a variable, water and juice are “values” of the variable and not variables themselves.
 * 1) Students are not expected to know which variables, out of all possible variables, could be related to the outcome of an experiment.
 * 2) Students are not expected to know that it may not be possible to control or even identify all relevant variables in an experiment. These ideas are included in 1B/M2b and 1B/H3. However, when given a set of variables, students are expected to know that in order to determine if there is a relationship between a particular variable and an outcome, all other variables in the set must remain constant.
 * 3) Students are not expected to know when they can or cannot generalize the results of an experiment beyond the given experimental and control groups.
 * 4) Students are not expected to know the terms "independent" and "dependent" variables.
 * Item Type A1: Given an idea to be tested (hypothesis) and an experimental setup, explain why certain variables are (or should be) kept constant.

Percent of students answering correctly (click on the item ID number to view the item and additional data)||~ Item ID Number ||~ Knowledge Being Assessed 6–8 ||~ Grades 9–12 ||~ Select This Item for My Item Bank ||
 * ~ Grades
 * [|CV015005] || [|To find out which car gets better gas mileage, it is important that both cars get the same grade of gas because if they didn't, it wouldn't be possible to tell which car gets the better gas mileage.] || 53% || 66% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1075"]] ||
 * [|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.] || 51% || 69% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1074"]] ||
 * [|CV005004] || [|To find out the effect of paper type on how well paper airplanes fly, it is important that all the airplanes tested use the same design because if they didn't, it wouldn't be possible to tell what effect the type of paper had on how well the paper airplanes fly.] || 53% || 66% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1072"]] ||
 * [|CV013003] || [|To find out if the type of swimsuit swimmers wear affects a swim team's performance, it is important that everyone wear the same kind of swim cap because otherwise it wouldn't be possible to find out the effect of the swimsuits on the team's performance.] || 49% || 65% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1073"]] ||
 * [|CV012003] || [|To find out if the shape of objects has an effect on how fast the objects sink, it is important that all the objects tested have the same mass because if they didn't have the same mass, it wouldn't be possible to learn about the effect of shape on how fast they sink.] || 45% || 62% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1076"]] ||
 * [|CV016003] || [|To determine the effect of water temperature on getting stains out of shirts, it is important for all shirts to be washed for the same length of time because if they weren't, it wouldn't be possible to find out the effect of temperature.] || 44% || 54% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1078"]] ||
 * [|CV015006] || [|To determine the effect of speed on a truck's gas mileage, is important that trucks of the same weight be compared because if the trucks didn't have the same weight, it wouldn't be possible to learn about the effect of speed on gas mileage.] || 41% || 54% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1077"]] ||

Frequency of selecting a misconception||~ Misconception ID Number 6–8 ||~ Grades 9–12 || Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.
 * ~ Student Misconception ||~ Grades
 * [|CVM026] || [|A given experiment can test for the effects of everything that is included in the study, whether these variables are allowed to vary or are held constant.] || 26% || 19% ||
 * [|CVM011] || [|A given experiment tests for the effects of ALL related variables, regardless of whether they are allowed to vary or are held constant (AAAS Project 2061, n.d.).] || 26% || 19% ||
 * [|CVM018] || [|A given experiment tests for the effect of a variable that remains constant while other variables change (AAAS Project 2061, n.d.).] || 18% || 13% ||
 * [|CVM027] || [|It is not important to hold a variable constant in an experimental study if the purpose of the study is not to find out the effect of that variable on the outcome of the study.] || 8% || 6% ||
 * [|CVM013] || [|When testing the effect of a variable on the outcome of the experiment, it does not matter if other relevant variables change at the same time (AAAS Project 2061, n.d.)] || 8% || 6% ||

==== If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables. -and- Item Type A2: Select an experimental setup to test the effect of a variable on the experimental outcome, when all relevant variables are provided. ==== These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below. > //Students are expected to know that:// //Boundaries//: > This is an item type. There are no sub-ideas.
 * [|Sub-Ideas]
 * [|Items & Student Performance]
 * [|Misconceptions]
 * If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables.
 * 1) By changing a single variable at a time and holding all other relevant variables constant it is possible to determine whether that single variable is correlated with the outcome or not.
 * 2) When varying more than one variable at a time it is not possible to determine the correlation between either variable and the outcome of an experiment.
 * 3) The reason for controlling a particular variable (holding it constant) in an experiment is because it may have an effect on what is being tested.
 * 4) A variable is an entity that may assume different values, either quantitative or qualitative, not a particular value of a variable. For example, when “types of liquid” is defined as a variable, water and juice are “values” of the variable and not variables themselves.
 * 1) Students are not expected to know which variables, out of all possible variables, could be related to the outcome of an experiment.
 * 2) Students are not expected to know that it may not be possible to control or even identify all relevant variables in an experiment. These ideas are included in 1B/M2b and 1B/H3. However, when given a set of variables, students are expected to know that in order to determine if there is a relationship between a particular variable and an outcome, all other variables in the set must remain constant.
 * 3) Students are not expected to know when they can or cannot generalize the results of an experiment beyond the given experimental and control groups.
 * 4) Students are not expected to know the terms "independent" and "dependent" variables.
 * Item Type A2: Select an experimental setup to test the effect of a variable on the experimental outcome, when all relevant variables are provided.

Percent of students answering correctly (click on the item ID number to view the item and additional data)||~ Item ID Number ||~ Knowledge Being Assessed 6–8 ||~ Grades 9–12 ||~ Select This Item for My Item Bank ||
 * ~ Grades
 * [|CV004003] || [|An experiment in which the number of fish in a series of fish bowls is held constant and the temperature of the water in the fish bowls is varied could tell you the effect that water temperature has on the behavior of goldfish.] || 66% || 83% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1067"]] ||
 * [|CV006003] || [|An experiment in which the amount of bleach and the size of a stain on a shirt were held constant, and the type of bleach varied, could tell you which of two bleaches was better at removing stains.] || 67% || 79% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1068"]] ||
 * [|CV002003] || [|An experiment in which the amount of sunlight is varied and the minerals in the plant's water is held constant could tell you the effect of light on plant growth.] || 63% || 78% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1066"]] ||
 * [|CV024005] || [|An experiment in which variable X is allowed to vary and variables Y and Z are held constant could tell you if variable X has an effect on the result of the experiment.] || 44% || 59% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1069"]] ||
 * [|CV001003] || [|A carts and ramp experiment in which the weight of the carts is varied and the height of the ramp is held constant could tell you the effect of the weight of the cart on the cart's speed.] || 43% || 56% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1065"]] ||

Frequency of selecting a misconception||~ Misconception ID Number 6–8 ||~ Grades 9–12 || Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.
 * ~ Student Misconception ||~ Grades
 * [|CVM013] || [|When testing the effect of a variable on the outcome of the experiment, it does not matter if other relevant variables change at the same time (AAAS Project 2061, n.d.)] || 25% || 17% ||
 * [|CVM010] || [|In order to determine whether a certain variable has an effect on the outcome, one must keep this variable constant and change other related variables (Tschirgi 1980, Zimmerman & Glaser 2001). (Note: This is especially true in situations where the control experiment produced a favorable outcome.)] || 21% || 16% ||
 * [|CVM009] || [|In order to determine whether a certain variable has an effect on the outcome, one must vary ALL variables at the same time (Tschirgi 1980).] || 19% || 12% ||
 * [|CVM021] || [|When testing for the effect of a particular variable on an outcome, it is important for that variable to vary, but only one other relevant variable has to be controlled and the rest can vary.] || 15% || 10% ||

==== If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables. -and- Item Type A3: Identify the variable(s) being tested in a given controlled experimental setup. ==== These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below. > //Students are expected to know that:// //Boundaries//: > This is an item type. There are no sub-ideas.
 * [|Sub-Ideas]
 * [|Items & Student Performance]
 * [|Misconceptions]
 * If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables.
 * 1) By changing a single variable at a time and holding all other relevant variables constant it is possible to determine whether that single variable is correlated with the outcome or not.
 * 2) When varying more than one variable at a time it is not possible to determine the correlation between either variable and the outcome of an experiment.
 * 3) The reason for controlling a particular variable (holding it constant) in an experiment is because it may have an effect on what is being tested.
 * 4) A variable is an entity that may assume different values, either quantitative or qualitative, not a particular value of a variable. For example, when “types of liquid” is defined as a variable, water and juice are “values” of the variable and not variables themselves.
 * 1) Students are not expected to know which variables, out of all possible variables, could be related to the outcome of an experiment.
 * 2) Students are not expected to know that it may not be possible to control or even identify all relevant variables in an experiment. These ideas are included in 1B/M2b and 1B/H3. However, when given a set of variables, students are expected to know that in order to determine if there is a relationship between a particular variable and an outcome, all other variables in the set must remain constant.
 * 3) Students are not expected to know when they can or cannot generalize the results of an experiment beyond the given experimental and control groups.
 * 4) Students are not expected to know the terms "independent" and "dependent" variables.
 * Item Type A3: Identify the variable(s) being tested in a given controlled experimental setup.

Percent of students answering correctly (click on the item ID number to view the item and additional data)||~ Item ID Number ||~ Knowledge Being Assessed 6–8 ||~ Grades 9–12 ||~ Select This Item for My Item Bank ||
 * ~ Grades
 * [|CV030001] || [|In an experiment involving three variables (X, Y, and Z) that could affect the outcome of the experiment, changing X and keeping Y and Z constant allows you find out the effect of X on the outcome of the experiment.] || 57% || 79% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1071"]] ||
 * [|CV018002] || [|A controlled experiment involving the drying of swimsuit fabric, in which the type of fabric changes but how large a piece of fabric you use and how wet the fabrics are to start with are held constant, can tell you if the type of fabric affects how long it takes the fabrics to dry.] || 56% || 68% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1080"]] ||
 * [|CV019002] || [|A controlled experiment involving the floating of clay boats, in which the shape of the boats varies and the weight of the boats stays the same, can tell you if shape affects the floating of the boats.] || 50% || 64% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1079"]] ||
 * [|CV023005] || [|In an experiment involving two variables (X and Y) that could affect the outcome of the experiment, changing X and keeping Y constant allows you to find out the effect of X on the outcome of the experiment.] || 42% || 60% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1070"]] ||
 * [|CV017002] || [|A controlled experiment involving the behavior of fish in fish bowls, in which the number of fish in the bowls varies and the temperature of the water and the amount of light is held constant, allows you find out the effect of the number of fish on fish behavior.] || 37% || 58% || [[image:http://assessment.aaas.org/img/star_16x16_grey.png link="http://assessment.aaas.org/users/itembank/add/1081"]] ||

Frequency of selecting a misconception||~ Misconception ID Number 6–8 ||~ Grades 9–12 || Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.
 * ~ Student Misconception ||~ Grades
 * [|CVM026] || [|A given experiment can test for the effects of everything that is included in the study, whether these variables are allowed to vary or are held constant.] || 32% || 22% ||
 * [|CVM011] || [|A given experiment tests for the effects of ALL related variables, regardless of whether they are allowed to vary or are held constant (AAAS Project 2061, n.d.).] || 29% || 19% ||
 * [|CVM028] || [|A controlled experiment tests for the effect of variables that are held constant, not the variable that is allowed to change.] || 21% || 14% ||

==== If more than one variable changes at the same time in an experiment, the outcome of the experiment may not be clearly attributable to any one of the variables. -and- Item Type A4: Given an experiment with two variables changing at the same time, determine that no conclusion can be drawn regarding the effect of each individual variable. ====
 * [|Sub-Ideas]
 * [|Items & Student Performance]
 * [|Misconceptions]