Independent Variables, Dependent Variables & Hypotheses

A Variable is anything that can change in an experiment. There are three types of variables that an experimenter must deal with when designing an experiment. Independent Variable Dependent Variable Controlled Variables

What is tested or manipulated. Independent Variable Something that is changed by the scientist during an experiment or investigation What is tested or manipulated.

The data collected during the investigation Dependent Variable Something that might be affected by the change in the independent variable What is observed What is measured The data collected during the investigation

Controlled Variables Any variables that are not changed during an experiment Also called constants Allows for a “fair test”

Example 1 Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle. Identify the variables in this experiment & write a hypothesis for the experiment.

What was the independent variable? Ages of the students Different ages were tested by the scientist

What was the dependent variable? The time it took each student to put their puzzle together The time was observed and measured by the scientist

What was one controlled variable? Same puzzle All of the participants were tested with the same puzzle. It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

What is a hypothesis for this experiment? It must be testable & it could have a negative outcome. Is this a good hypothesis? Ohio State is the best college football team to ever play. No – there is no test you could run that would have a possible negative outcome.

What is a hypothesis for this experiment? It is best to write a hypothesis as an “If, then” statement. If you give the same puzzle to an older student, then that student will put the puzzle together in less time than a younger student.

Example 2 An investigation was done with an electromagnetic system made from a battery and wire wrapped around a nail. Different lengths of nails were used. The number of paper clips the electromagnet could pick up was measured. Identify the variables in this experiment & write a hypothesis for the experiment.

What was the independent variable? Size of the nails used These were changed by the scientist

What was the dependent variable? Number of paper clips picked up by the nail. The number of paper clips was observed and counted (measured).

What were some of the controlled variables? Battery, wire, type of nail None of these items were changed.

What is a hypothesis for this experiment? It must be testable & it could have a negative outcome. It is best to write a hypothesis as an “If, then” statement. If you wrap wires identically around different length nails, then the longer nails will pick up more paperclips .