2 Experimental Design and Variables Free Online FlashCards

What should a clear experimental question identify?

A clear experimental question identifies the factor to change and the outcome to measure.

What makes an experimental procedure reproducible?

A procedure should describe materials, steps, measurements, and number of trials clearly enough for someone else to repeat the investigation.

What is the independent variable?

The independent variable is the factor deliberately changed by the experimenter.

Why change one factor at a time in a simple experiment?

Changing one factor at a time makes it more likely that a measured difference is related to the factor being tested.

How does a control condition differ from a controlled variable?

A control group or condition provides a comparison for the experimental group; a controlled variable is a condition kept the same.

What is measurement error?

Measurement error is a difference between a measured result and the true value, such as reading a ruler at an angle or using an imprecise tool.

How can random assignment improve an experiment?

When practical, randomly assigning samples to groups can help prevent pre-existing differences from favoring one group.

When does an outcome difference support a conclusion about the changed factor?

A difference in the measured outcome supports a conclusion about the changed factor only insofar as the design controlled plausible alternative explanations.

What is the dependent variable in the fertilizer example?

The dependent variable is the outcome measured. In the plant example, it is height measured after four weeks.

What are controlled variables?

Controlled variables are relevant conditions kept the same, such as plant species, soil type, pot size, water, light, and growing time.

What could serve as the control condition in a fertilizer experiment?

Plants receiving no fertilizer can serve as the control condition, provided they receive the same soil, water, light, and care as the fertilized plants.

What is the purpose of a positive control?

A positive control is expected to produce a known effect; it checks whether the procedure can detect that effect.