Transcript Introduction to Experimental Design-2011

AP Biology
Science
 A way of learning about
the natural world
 Includes all of the
knowledge gained by
exploring the natural
world
 This knowledge is
always growing and
changing as scientists
ask new questions and
explore new ideas
Scientific Inquiry
 Scientific: Of or relating to the practice of science
 Inquiry: A close examination of a matter in a search
for information or truth
 Scientific Inquiry: The ways in which scientists
explore the natural world
How Does Scientific Inquiry
Work?
 Scientific Method:
 Make observations
and/or inferences
 Ask questions
 Develop hypotheses
 Design experiments
 Make measurements
 Collect data
 Interpret data
 Draw conclusions
 Communicate
Make Observations and Inferences
 Observation: Using one or more of your senses to
collect data
 Inference: An interpretation of an observation that is
based on evidence or prior knowledge
 Data: Facts, figures and other evidence gathered
through observation
Question
 You ask a question
about what you
observe.
 State the problem or
question.
 Example: Does the drop
height affect the bounce
height of a superball?
Developing a Hypothesis
 Hypothesis: A possible explanation for a set of
observations or answer to a scientific question
 A hypothesis must be something that can be tested
 Worded as an If . . . Then statement
 Hypotheses can either be supported or disproved
 Example: If a superball is dropped from increasing
heights then the bounce heights will also increase
because…
Null Hypothesis
 A hypothesis that can be rejected-it essentially states
that the variables will have no effect on the outcome of
the experiment
 Why use a Null Hypothesis?
 You can never have enough support for a hypothesis to
say that it is the sole explanation of a phenomenon, but
you can have enough data to show that it is not the sole
explanation of a phenomenon.
Designing an experiment to
test a hypothesis
 After you state your hypothesis, you must design an
experiment to test it.
 You figure out a way to test whether the hypothesis is
supported.
 Control group– nothing changed
 Experimental group – one variable changed
 The outcome must be measurable (quantifiable).
 Record and analyze data.
Designing a Controlled Experiment.
 An experiment in which all of the variables except
for one are remain the same
 An experiment that is designed to compare an
experimental group with a control group.
 Ideally, a control group and an experimental group
differ in only one variable.
 Control group serves as a comparison to measure
against
Experiment Variables
 Variable: Factors that can change in an experiment
 Manipulated (Independent) Variable: The variable
that is changed during the experiment
 Responding (Dependent) Variable: The factor that
changes because of the manipulated variable
 Variable that is measured in the experiment
Variables
 Independent variable
 Example: Does the drop height affect the bounce height
of a superball?

We know the drop heights we will use.
 Dependent variable
 Example: Does the drop height affect the bounce height
of a superball?

We don’t know the bounce height before we start. It is what is
being measured.
Constants
 Constant: a variable that does not change for the
duration of an experiment; a value that remains the
same
 Examples: Does the drop height affect the bounce height
of a superball?

The superball does not change during the experiment. The
same force is applied during each trial.
Interpreting Data
 You do the experiment using the
method you came up with and
record the results.
 After the data are collected, they
must be organized and
interpreted
 Create data tables, graphs to
represent data
 Perform calculations that will
determine what results mean
(averages, percentages, totals)
 Identify possible sources of
errors
Drawing Conclusions
 After you have
organized and
interpreted your data,
you must draw a
conclusion.
 You need to decide if
the data support your
original hypothesis.
Retest
 In order to verify the results, experiments must be
retested.
Communicating
 Scientists must communicate their findings to other
scientists.
 This contributes to the growth of the body of
 scientific knowledge.
Scientific Theories
 Scientific Theory: A well-tested concept that
explains a wide range of observations.
 A theory is based on thousands of experiments done
by different scientists.
 A theory is much broader in scope than a
hypothesis.
 Theories only become widely accepted in science if
they are supported by an accumulation of extensive
and varied evidence.
 Future testing may prove a theory to be incorrect.