Scientific Methodology:
Ø Scientific methodology involves:
1. 
2. 
3. 
4. 
observing and asking questions
making inferences
forming hypotheses
conducting controlled
experiments
5.  collecting and analyzing data
6.  drawing conclusions.
Observing and Asking Questions
Ø Scientific investigations begin with observation,
the act of noticing and describing events or
processes in a careful, orderly way.
Ø For example, researchers observed that marsh
grass grows taller in some places than others.
This observation led to a question: Why do
marsh grasses grow to different heights in
different places?
Inferring and Forming a Hypothesis
Ø After posing questions, scientists use further
observations to make inferences, or logical
interpretations based on what is already known.
Ø Inference can lead to a hypothesis, or a scientific
explanation for a set of observations that can be
tested in ways that support or reject it.
Inferring and Forming a Hypothesis
Ø For example, researchers inferred that
something limits grass growth in some places.
Based on their knowledge of salt marshes, they
hypothesized that marsh grass growth is limited
by available nitrogen.
A hypothesis is an “educated guess.” Designing Controlled Experiments
Ø Testing a scientific hypothesis often involves
designing an experiment that keeps track of various
factors that can change, or variables. Examples of
variables include temperature, light, time, and
availability of nutrients.
Ø Whenever possible, a hypothesis should be tested
by an experiment in which only one variable is
changed. All other variables should be kept
unchanged, or controlled. This type of experiment is
called a controlled experiment.
Controlling Variables
Ø It is important to control variables because if several
variables are changed in the experiment,
researchers can’t easily tell which variable is
responsible for any results they observe.
Ø The variable that is deliberately changed is called
the independent variable.
Ø The variable that is observed and that changes in
response to the independent variable is called the
dependent variable.
Control and Experimental Groups
Ø Typically, an experiment is divided into control
and experimental groups.
Ø A control group is exposed to the same
conditions as the experimental group except for
one independent variable.
Ø Scientists set up several sets of control and
experimental groups to try to reproduce or
replicate their observations.
Designing Controlled Experiments
Ø For example, the researchers selected similar plots
of marsh grass. All plots had similar plant density,
soil type, input of freshwater, and height above
average tide level. The plots were divided into
control and experimental groups.
Ø The researchers added nitrogen fertilizer (the
independent variable) to the experimental plots.
They then observed the growth of marsh grass (the
dependent variable) in both experimental and
control plots.
Collecting and Analyzing Data
Ø Quantitative data are numbers obtained by counting or
measuring.
Ø Data is usually recorded in a table, which can then be
transferred to a graph.
No added nitrogen 50g Nitrogen/
M2 Day 7 2 cm 2 cm Day 14 9 cm 12 cm Day 21 18 cm 67 cm Day 28 21 cm 84 cm Graphing
Ø This graph shows how grass height changed
over time.
Drawing Conclusions
Ø Analysis showed that marsh grasses grew
taller than controls by adding nitrogen.
Graphing Variables
I.V. (x) D.V. (y) In most cases, the independent variable is ploFed along the x-­‐axis, and the dependent variable is ploFed along the y-­‐axis. However, if measurements are taken over Mme, Mme is usually ploFed along the x-­‐axis. 8/31/15 Drawing Conclusions
Ø New data may indicate that
the researchers have the right
general idea but are wrong
about a few particulars. In that
case, the original hypothesis
is reevaluated and revised;
new predictions are made,
and new experiments are
designed.
Ø Hypotheses may have to be
revised and experiments
redone several times before a
final hypothesis is supported
and conclusions can be
drawn.
Scientific Methodology
•  Science is “a way of knowing.”
•  All science begins with an
observation.
•  A hypothesis is an educated
guess.
•  A controlled experiment
requires:
–  An experimental group
–  A control group
•  The goal of the experiment is
to confirm or deny the
hypothesis.
Vocabulary Building 8/31/15 •  Mass –  A quan)ty of ma/er –  Measured in kilograms –  Not the same as weight (gravity’s downward pull) •  Length –  The longest dimension of an object –  Measured in meters Vocabulary Building 8/31/15 •  Volume –  A measure of how much space something takes up –  Measured in liters or in cubic meters (m3) –  Ex: one liter equals 1000 cm3 •  Density –  Amount of mass per unit of volume –  Number of objects in an area (ex: popula)on density –  Density = mass/volume 8/31/15 Vocabulary Building 8/31/15 •  Hypothesis –  A supposi)on or proposed explana)on made on the basis of limited evidence as a star)ng point for further inves)ga)on –  An educated guess •  Scien)fic Theory –  A well tested explana)on of some aspect of the natural world that is acquired through the scien)fic method and repeatedly tested and confirmed through observa)on and experimenta)on, and enables scien)sts to make accurate predica)ons about new situa)ons •  Law –  A statement based on repeated experimental observa)ons that describes some aspects of the universe. A scien)fic law always applies under the same condi)ons and implies that there is a causal rela)onship involving its elements.