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
1 2 3 4 5 8 7 6 9 10 11 12 13 14 15
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
Steps in the Scientific Method • Observe • Ask Questions, State the Problem • Form a hypothesis Hypothesis = a possible explanation that can be tested by experimentation • Design a controlled experiment
Controlled Experiments should have: • Independent variable – factor manipulated by the experimenter (on x axis of graph) • Dependent variable – factor that responds to the independent variable (on y axis of graph) • Control group – used as a standard of comparison • Experimental group(s) – exposed to the independent variable
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 • Analyze data • Publish results (results should be repeatable) • Form a theory (possibly) A theory is a generally accepted scientific principle
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?
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: • Did not have any measurements • Did not have a hypothesis • Was not made by a scientist • Was not repeatable