Designing a Controlled Experiment
(from Laurie Cripe)
PARTS
Question
Elements to include
Identifies the manipulated variable (what was changed)
Identifies the responding variable (what was measured)
Asks about a relationship between the two variables – “ How does (the
manipulated variable) affect (the responding variable)?”
Ends with a question mark.
Hypothesis
Uses “If____, then____ because____” format.
Predicts the relationship between the variables in the question.
Identifies the directionality of the result (increase, decrease, etc.).
Offers reasons for prediction.
Procedure
Lists materials (including amounts and measures) needed to do
investigation.
Includes a detailed list of numbered steps that will be followed in the
investigation. Includes any safety procedures.
Identifies the variable that will be manipulated (changed) and what
responding variable will be measured.
Only one manipulated variable at a time.- all other variables should be
kept unchanged (controlled).
States to repeat steps to ensure reliable results and states to record the
data.
Data
Displays observations and measurements neatly and orderly.
Labels manipulated and responding variables (with units)
Completes calculations accurately
Summarizes data appropriately.
Conclusion
(i.e. averages, graphs)
Answers the investigative question. (discusses whether hypothesis was
correct)
Provides supporting data for the lowest condition and the highest
condition.
Explains how the data support a correct conclusion using comparative
language (smallest, only, larger than, etc.)
Checking Your Experimental Design
 Does the title clearly identify both the manipulated and responding variables?
 Does the question include both the manipulated and responding variables?
 Does the hypothesis clearly state how you think changing the manipulated variable
will affect the responding variable?
 Is there just one manipulated variable? Is it well defined?
 Are the changes of the manipulated variable clearly stated? Are there enough
changes tested? Are there too many?
 Is there a control? Is it clearly stated?
 Are there repeated trials? Are there enough of them? Too many?
 Is the responding variable clearly identified and is it clearly defined? (Is it clear how
the measure will be taken or described?)
 Are the constants (controlled variables) clearly identified and described?
 Do you include a diagram to help clarify the procedure?
 Is your experiment creative? Does it have an appropriate level of complexity?