Experimental Design

Remember the Scientific Method

Problem/Question

Observation/Research

Formulate a Hypothesis

Experiment

Collect and Analyze Results

Conclusion

Communicate the Results

State the Problem/Question You Observed

• 1. Qualitative

– Uses the 5 senses, opinion

– Describes qualities

• 2. Quantitative

– Using equipment, standard units

– Uses numbers

Research to Form a Hypothesis

• Hypothesis – an educated guess or prediction stated in “If…..then….” form that is TESTABLE.

• Forming a valid hypothesis requires background research – Scientific Journals: for current research findings

– Encyclopedias: for scientific info generally accepted

– State and Local research facilities

Predicting

• To test hypothesis it is necessary to make predictions that logically follows from the hypothesis

• A statement made in advance that states the results that will be obtained from testing the hypothesis

• Deductive reasoning = Often in the form of an “if-then” statement; reasoning goes from general information to a specific hypothesis

• Inductive reasoning = reasoning from a particular set of facts to form a general rule; specific to general

The Experiment

• Is a structured procedure to test hypothesis.

• All good experiments include the following five elements:

– 1. Independent Variable

– 2. Dependent Variable

– 3. Constants

– 4. Control

– 5. Repeated Trials

The 5 Elements of an Experiment

Independent Variable (IV) - the factor that is purposely changed by the experimenter (there is only one IV per experiment)

- The thing that “I” change or manipulate

- There is only 1 IV per experiment

The 5 Elements of an Experiment • Dependent Variable (DV) -

the factor that is expected to change and will be measured.

• The measurement may result in data that is quantitative or qualitative.

– The thing that is measured or observed, the measurement that “depends” on what we change.

The 5 Elements of an Experiment

• Constants - the factors that are kept the same among ALL test groups including the experimental groups and control groups.

• Control Group the group used as a standard for comparison; it receives no treatment (IV).

– Used as a baseline measurement to compare.

The 5 Elements of an Experiment

• Repeated Trials – redoing the experiment to rule out error.

– Used as a “check” to see if the experiment is sound.

OR

Constructing Graphs

• Title the Graph

– The effect of (IV) on (DV)

• Label the Axes with Units!

– (IV) on the x-axis

– (DV) on the y-axis

• Determine the scale for axes

– Consistent intervals, starting at zero

Graph

• Don’t forget Units!!!!!!

Title

(IV) Independent Variable

(DV) Dependent

Variable

Conclusions & Discussion of Results

• In all formal experiments, scientists summarize their findings and analyze their data.

• They discuss problems during experiment.

• They offer suggestions for improvements for future experiments.

Scientific Method

a series of steps used to solve a problem

Scientific Method Notes

People In Hawaii Eat Old Coconuts

1. Problem = what you are trying to solve

2. Information = research or past

experiences

3. Hypothesis = an educated guess based

on information that is testable

4. EXPERIMENT = test your hypothesis a) Controlled experiment = has at least two identical setups

Control group = group used for comparing results

Experimental group = group in which you change one variable

b) Variable = the factor that you change <only one at a time>

independent variable = the part that you as the experimenter setup to test or change in the experiment

* manipulative variable

* goes on the x-axis

dependent variable = the observations/measurements that you write down when you do the experiment

* the results of the experiment

* data, measurements, responses

* goes on the y-axis

How to graph the variables:

c) constants = factors that remain the same and have fixed

values

d) control = what you compare your experimental results to

e) repeated trails = repeat experiments at least 3 times

5. Observations/Record Data = write down what occurs during the experiment, measurements, graphs, charts

Qualitative data = observations using your senses

Quantitative data = number measurements

6. Conclusion = whether your data supports your hypothesis

Hypothesis:

Theory:

Scientific law:

If a question is not testable using the scientific method….

Then it is not Science!!!!!

Sample Experiment

• An ecologist with the Environmental Protection Agency (EPA) wants to investigate the effects of acid rain on the reproductive rate of salamanders. The scientist incubates 1000 salamander eggs in mildly acidic water (pH = 6) and another 1000 salamander eggs in neutral water (pH = 7). The water temperature, amount of dissolved oxygen, and light was kept the same among all groups. All eggs were given 63.days to develop.

• Independent Variable:

– the pH of the water

• Dependent Variable:

– the development of salamander eggs

• Constants:

– water temperature, dissolved oxygen, light, and time

• Control Group:

– 1000 eggs in neutral water

• Trials:

– 1000 eggs in mildly acidic water

Experimenting

• Testing a hypothesis or prediction by

gathering data under controlled conditions

– conducting a controlled experiment

• Based on a comparison of a control

group with an experimental group

– Both groups are identical except for one

factor (independent variable or

manipulative variable)

– Observations and measurements are taken

for a particular factor (dependent variable)

in both groups

Collecting Data

• Includes any and all information that scientist gather in trying to answer their questions

• Includes all measurements & observations made during the experiment

• Qualitative data = observe with senses

• Quantitative = number measurements

–Measuring

• Involves quantitative data that can be

measured in numbers

–Sampling

• Technique of using a sample – a

small part – to represent the entire

population

Subjective = opinion

Objective = actual measurements/facts

Organizing Data

• Involves placing observations and

measurement (data) in order

– Graphs, charts, tables, or maps

Analyzing Data

• Collected and organized data must be

analyzed

– Process of determining whether data are

reliable or whether they support or do not

support a hypothesis or prediction

Inferring

• Conclusions made on the basis of facts or

premises rather than on direct

observations

– Often drawn from data gathered from a

study or experiment and previous

knowledge

– Not directly testable

Forming a Theory

• A theory may be formed after many related hypotheses have been tested and supported with experimental evidence

• A broad and comprehensive statement of what is thought to be true

• Supported by considerable evidence

• Ties together related hypotheses

• If never proven wrong over time, a theory can become a scientific law

Communication

• Share the results of their studies with other scientists

• Publish findings in journals or at scientific meetings

• Sharing of information is essential to scientific process

• Subject to examination and verification by other scientists

• Allows scientists to build on the work of others