ExperimentationExperimentation

VariablesVariables

Variable = an aspect of events or things Variable = an aspect of events or things that differs according to the particular event that differs according to the particular event or thing being considered but has a or thing being considered but has a particular value for a given event or thing at particular value for a given event or thing at a given timea given time

Ex. Variable = weight Things = persons Ex. Variable = weight Things = persons Different persons weigh different amounts Different persons weigh different amounts but a single person weighs a certain but a single person weighs a certain amount at a given time.amount at a given time.

Variables are PervasiveVariables are Pervasive

Every dimension by which an entity or Every dimension by which an entity or event can be described can be event can be described can be considered a variable.considered a variable.

Experiments and VariablesExperiments and Variables

Experiments are conducted to attempt Experiments are conducted to attempt to find out the relationships among to find out the relationships among variables.variables.

Quantifying VariablesQuantifying Variables

Variables can be quantified by Variables can be quantified by measuring their different values.measuring their different values.

Functional RelationshipsFunctional Relationships

Variables are functionally related when Variables are functionally related when the value of one variable determines the value of one variable determines another.another.

This can be stated mathematically: This can be stated mathematically: Y = f (X). The value of the variable Y is Y = f (X). The value of the variable Y is a function of the value of the variable X.a function of the value of the variable X.

Ex. Running Speed = f (weight carried)Ex. Running Speed = f (weight carried)

Experimental DesignExperimental Design

Experiments must be carefully designed Experiments must be carefully designed to determine the functional relationships to determine the functional relationships among variables.among variables.

The influence of variables other than The influence of variables other than those being tested must be controlled.those being tested must be controlled.

Experimental VariablesExperimental Variables

Independent VariablesIndependent Variables Dependent VariablesDependent Variables Control VariablesControl Variables

Independent VariablesIndependent Variables

Directly manipulated by the Directly manipulated by the experimenter and determined before the experimenter and determined before the experiment beginsexperiment begins

Experiments are designed to see how Experiments are designed to see how manipulating the independent variable manipulating the independent variable will effect the dependent variable.will effect the dependent variable.

Example of an Independent Example of an Independent VariableVariable

A runner is clocked sprinting for 100 A runner is clocked sprinting for 100 yards with a backpack 6 times carrying yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds.0, 10, 20, 30, 40 and 50 pounds.

The weight in the backpack is the The weight in the backpack is the independent variableindependent variable

Dependent VariablesDependent Variables

The values of the dependent variable The values of the dependent variable are the product of the experimental are the product of the experimental conditions.conditions.

They are a function of the values of the They are a function of the values of the independent variable.independent variable. Dependent = f (Independent)Dependent = f (Independent)

They are measured under each of the They are measured under each of the values of the independent variable.values of the independent variable.

Example of a Dependent Example of a Dependent VariableVariable

A runner is clocked sprinting for 100 A runner is clocked sprinting for 100 yards with a backpack 6 times carrying yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds.0, 10, 20, 30, 40 and 50 pounds.

The runner’s speed is the dependent The runner’s speed is the dependent variablevariable

Control VariablesControl Variables

Control variables are set so that they Control variables are set so that they cannot systematically affect the cannot systematically affect the relationship between the independent relationship between the independent and dependent variables.and dependent variables.

The average value of a control variable The average value of a control variable should not change as the independent should not change as the independent variable changes.variable changes.

Example of Control VariablesExample of Control Variables

A runner is clocked sprinting for 100 A runner is clocked sprinting for 100 yards with a backpack 6 times carrying yards with a backpack 6 times carrying 0, 10, 20, 30, 40 and 50 pounds.0, 10, 20, 30, 40 and 50 pounds.

The time that the 6 races are run is a The time that the 6 races are run is a control variable and should be set so control variable and should be set so that the runner doesn’t get more and that the runner doesn’t get more and more tired with each race.more tired with each race.

Ways of Setting Control Ways of Setting Control VariablesVariables

Have no variation of the control variable Have no variation of the control variable among different experimental conditions.among different experimental conditions.

Have the same distribution of the control Have the same distribution of the control variable among the different variable among the different experimental conditions.experimental conditions.

Have the values of the control variable Have the values of the control variable randomly assigned among the different randomly assigned among the different experimental conditions.experimental conditions.

Variables and HypothesesVariables and Hypotheses

Experimental scientists must try to Experimental scientists must try to relate some terms of a hypothesis to relate some terms of a hypothesis to dependent variables and some of them dependent variables and some of them to independent variables.to independent variables.

Hypothesis TestingHypothesis Testing

A well designed experiment will permit A well designed experiment will permit observations under controlled observations under controlled conditions and reveal the relationship conditions and reveal the relationship between independent and dependent between independent and dependent variables and thus of the hypothetical variables and thus of the hypothetical terms.terms.