Observation vs. Inference
• Observation: the act of noting or
perceiving objects or events using the
senses
• Inference: a judgment based on reasoning
from evidence known or assumed to be
true
Observation or Inference?
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I think there is someone at the door
Inference
The child is happy
Inference
The liquid is colorless
Observation
The dog is scratching because it has fleas
Inference
The cat is afraid of the vacuum cleaner
Inference
Make an Inference
• Andruw Jones has 8 luxury cars
• The ice cream in the freezer is melted
• The doors to my favorite restaurant
were locked on Friday
• Jim was late to 1st period
• Traffic was worse than usual this
morning
Types of Observations
• Quantitative: Involve a number or
measurement
• The water has a temperature of 65º C,
the nickel has a mass of 5 g,
a dime is 1 mm thick, etc.
• Qualitative: Observations made using the
senses
• The wood smells like pine, I hear a loud
noise outside, the syrup feels sticky
The Scientific Method
Hydrangeas planted in my backyard
Hydrangeas in a Michigan yard
Steps in the Scientific Method
1. Make Observations
2. Ask Questions
3. Form a hypothesis
Hypothesis = a proposed explanation
that can be tested by observation or
experiment
4. Design a controlled experiment
Controlled Experiments should have:
a) Independent variable – factor
manipulated by the experimenter
(on x axis of graph)
b) Dependent variable – factor that
responds to the independent variable
(on y axis of graph)
c) Control group – used as a standard of
comparison
d) Experimental group(s) – exposed to
the independent variable
How would you set up an
experiment to test the
hydrangea hypothesis?
Several identical hydrangea plants,
each with soil of a different pH
pH 3
pH 5
pH 7
pH 9
pH 11
Monitor the color of flowers over a period of
several weeks or months
Sci. method steps continued
5. Analyze results
6. Draw conclusions and verify results
(results should be repeatable)
• Scientific Theory
A theory explains many related
observations and is supported by a
large body of evidence
What happens when people are
the subjects of an experiment?
Hawthorne Effect:
People behave in a different manner when
they are being observed
Placebo
An inactive substance used as
a control in an experiment
a)
b)
c)
d)
e)
f)
g)
An experiment was performed to determine the
effect of music on ivy plants. Two groups of plants
were set up. One received music 24 hours/day,
and the other was left in silence. All plants were
given equal light, water and minerals.
Independent variable?
Dependent variable?
Constant factors?
Control group?
Experimental group?
Qualitative observations?
Quantitative observations?
a)
b)
c)
d)
e)
f)
Radon is a radioactive gas that seeps into homes
from the soil. It is thought to be one of the leading
causes of lung cancer. A research team
investigated this problem by collecting data from
50 homes. They measured basement radon levels,
and noted how many people living in the homes had
lung cancer.
Independent variable?
Dependent variable?
Control group?
Experimental group?
Is a placebo needed?
Possible problems with the study?
A man states that he saw Bigfoot in an
isolated forest. He was alone and did not
take any pictures or collect any physical
evidence of Bigfoot. His observation is not
very scientific because it:
a)
b)
c)
d)
Did not have any measurements
Did not have a hypothesis
Was not made by a scientist
Was not repeatable