Designing a Controlled Experiment

1. Designing a Controlled Experiment Use this PPT to review the design of a controlled experiment.

2. Purpose The purpose of a controlled experiment is to establish a cause and effectrelationship between two variables.

3. Observation Every experiment begins with an observation. Most dairy cows are milked two to three times per day. On average, a cow will produce six to seven gallons of milk each day.

4. Question One overambitious farmer wants his cows to produce more milk so that he can make more money. Since cow growth hormones are known to increase cow mass, he wonders if they can also increase milk production.

5. Question The question in a controlled experiment is written in such a way as to include the cause and effect. How do growth hormones affect milk production in cows?

6. Questions Scientific questions can take many forms. For this class, I’d like you to consistently use the format on the previous slide.

7. Hypothesis The hypothesis in a controlled experiment again references the cause and effect AND includes a specific prediction about what will occur. If growth hormone IS USED, then milk production in cows WILL INCREASE.

8. Controlled Experiment Set up at least two groups. NOTE: The control set-up or the control group is commonly referred to as “the control.”

9. Controlled Experiment Contains 3 types of variables: Independent Variable = condition that is being modified by the experimenter [CAUSE] Dependent Variable = condition that changes as a result [EFFECT] Controlled Variables = all the conditions that are kept constant between the experimental and control groups.

10. Controlled Experiment

11. Data Collection Decide what data to collect AND create a data table BEFORE you begin!

12. Graphing Results Create an appropriate graph of the results. In our class it will usually be a line graph.

13. Analysis > Conclusion At this point the experimenter tries to make sense of the data in order to reach a conclusion. The conclusion answers the experimental question. Growth hormone increases milk production in cows.

14. Inference Sometimes inference is used when formulating conclusions. Inference = conclusion reached by indirect evidence, a logical interpretation based on observations (may not observe the conclusion directly to be true, but can logically say that it is true based on other observations) “Because the street is wet, I infer that it rained” * Add this term and its definition to your notes *

15. Discussion In a discussion, the experimenter describes the topic, experimental procedure, conclusion, data support, further explanation, hypothesis check, possible sources of error and suggestions for follow-up experiments.

16. Discussion DON’T WORRY ABOUT THE DISCUSSION IN THIS ACTIVITY. WE WILL WORK ON THE SPECIFICS OF WRITING ONE OF THESE SOON! 

17. Publication Don’t forget… publishing results Allows other scientists to build on what has already been done. Provides the opportunity for scientists to check other scientists’ work (called peer-review) ensuring the validity of conclusions.

18. Publication If other scientists do not achieve the same results, the initial experiment and its conclusion will be rendered faulty. This is called the “self-correcting” quality of science… which means it corrects itself (eventually) as part of the normal process. (add this term to your list)