Observational Studies, Experiments, Sample Surveys, and Census

 Observational Study ◦ Try to gather information without disturbing the scene being observed. ◦ Most helpful when the observer knows what to look for/objective in mind. ◦ Something is occurring to everyone (both groups). ◦ Draws conclusions about possible effect of a treatment on subjects where the assignments are outside the control of the invbestigator.

 To describe a group or situation.  Examples ◦ Crime scene ◦ In Chemistry, you need to observe the color, odor, etc…of a reaction ◦ Traffic flow for an industrial park/new neighborhood (counting cars/trucks) ◦ How animals behave in the wild (what they eat, when they hunt, etc…..)

An observational study. A small group of individuals selected because they represent the larger group. Does not rely on judgments. A survey that draws on a representative sample of the population of the survey. ◦ Population –entire group of individuals about which we want information ◦ Sample – the part of the population we actually collect data from .

 Usually we study a sample to find out something about a population.  Sometimes we study a population to find out something about a sample.  Ex – It is advertised that 4 out of 5 dentists recommend Crest. How many dentists in Westford might recommend Crest?  In this case, we know something about the population and want to draw a conclusion about a sample.

 Sample survey that attempts to include the entire population in the sample.  The procedure of systematically acquiring and recording information about the members of a given population.  A regularly occurring and official count of a particular population.

 Do something to individuals in order to see how they respond  Deliberately imposes different treatments on our subjects in order to observe their responses.  The act of conducting a controlled test or investigation (ACTIVE).  Any procedure that can be infinitely repeated; has a well defined set of outcomes.

 Find out whether the treatment causes a change in the response; testing of an idea.  Only experiments allow us to establish cause and effect.  In order to prove cause and effect, you MUST conduct an experiment.  BUT, keep in mind that due to ethical reasons often we cannot conduct an experiment.

 If the researcher wanted to test a current cancer drug against a new one that he/she suspects is much more effective, if he administers the suspected less effective drug to half the subjects he is knowingly hurting their chances for survival. So instead, an observational study must be done.

 If the researcher wanted to know if power lines caused leukemia in children he/she cannot expose children to magnetic fields. It is hard to compare cancer rates among children who happen to live in more and less exposed locations because leukemia is quite rare and locations vary in many other ways other than magnetic fields.

Please note – not all experiments are done in labs Other examples – Pepsi vs. CokeBottled Water Types of coffee “On the average” is sometimes used to conclude the big ideas. Chapter 3 focuses on Experiments

 1. Textbook: Pgs. 18 #15 and #16  2. Experiment vs. Observational Studies  3. Pgs. 12, 13 #7,8,9  4. Pgs. 17, 18 #12, 13, 14