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?• 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 Observations2. 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 11Monitor the color of flowers over a period of several weeks or months

Sci. method steps continued

5. Analyze results6. 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

PlaceboAn inactive substance used as a control in an experiment

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.

a) Independent variable?

b) Dependent variable?

c) Constant factors?

d) Control group?

e) Experimental group?

f) Qualitative observations?

g) Quantitative observations?

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.

a) Independent variable?b) Dependent variable?c) Control group?d) Experimental group?e) Is a placebo needed?f) 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) Did not have any measurements

b) Did not have a hypothesis

c) Was not made by a scientist

d) Was not repeatable