Experimental Variables

Variable

A variable is any condition that may cause a change in the system being studied. 

Controlled experiment:

 In a controlled experiment, only one variable is changed to ensure  that the effect of only that one variable can be measured. This allows for a clear comparison between the control and experimental groups.

Independent variable:

 The independent variable is changed by the experimenter in the design of the experiment. This variable is sometimes called the  “manipulated variable.”

Dependent variable:

The dependent variable is what changes as a result of the change in the independent variable. This variable is sometimes called the “responding variable.” How many.. How much…

Controlled variables:

 These are  variables that you think may change the outcome of the experiment, but since they are not being studied,  they need to be kept constant in each trial.

Hypothesis

 If you (IV), then DV, when (cc) remains constant

• If soapy water is dropped onto a coin, then the coin will hold less water compared to when H2O is dropped onto the coin when the coin and the state of it remains constant. 

Well written research question:

• states the independent and dependent variables in the experiment.  

•  “How does the pH of soil affect the number of strawberries produced by a strawberry plant?”

Is the experiment reliable or valid? 

• Reliable: data is repetitive

• Validity: accuracy, does it show what you expected?

Standard deviation: how much did we “wiggle” from the mean? 

• Small SD: no spread

• Large SD: large spread

• 2 SD’s are used because it means we are 95% sure data is true >68%

How to find the error bar?

• Low bar: mean - SD

• High bar: mean + SD

Data is not reliable if bars overlap