Observational and Experimental Studies

  In an observational study, the researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations. Observational Study

  “Motorcycle owners are getting older and richer” Data is collected on the ages and incomes of motorcycle owners in 1980 and 1988, then compared. The findings show considerable differences in ages and incomes Example of an Observational Study

  In an experimental study, the researcher manipulates one of the variables and tries to determine how the manipulation influences other variables. Experimental Study

  A study conducted at Virginia Polytechnic Institute divided female undergraduate students into two groups and the students perform as many sit-ups as possible in 90 seconds. The first group was told “do your best.” The second group was told to try to increase the number of sit-ups done each day by 10%. At the end of the study, the first group averaged 43 sit-ups. The second group averaged 56 sit-ups. The conclusion drawn was that students who were given specific goals did better than those who were not. Example of an Experimental Study

  What variable was being manipulated in the sit-up study?  Subjects should be randomly assigned to groups  When researchers use intact groups, it is called a quasi-experimental study More on experimental studies….

  The independent variable in an study is the one that is being manipulated by the researcher.  The independent variable is aka the explanatory variable.  The resultant variable is called the dependent variable or the outcome variable. Definitions

  A study conducted at Virginia Polytechnic Institute divided female undergraduate students into two groups and the students perform as many sit-ups as possible in 90 seconds. The first group was told “do your best.” The second group was told to try to increase the number of sit-ups done each day by 10%. At the end of the study, the first group averaged 43 sit-ups. The second group averaged 56 sit-ups. The conclusion drawn was that students who were given specific goals did better than those who were not. Identify the dependent and independent variables in this study

 In an experimental study, there are generally two groups:  The group that receives special conditions and is testing the independent variable is called the treatment group.  The group that receives no special conditions and is not testing the independent variable is called the control group. Definitions

 1.At JFK hospital, lung capacity is measured on all patients. A researcher gathers the information on women aged and compares smoking habits to the results of the lung capacity assessment. 2.A researcher is testing out a new shampoo that will make hair soft and manageable. She randomly assigns 20 women to two groups. One group tries the new shampoo for one month, and the other continues to use their own for the same time period. After one month, each women is asked to describe the softness and manageability of their hair. Identify whether each is an experimental or observational study. Then identify the independent and dependent variables

  The Hawthorne effect occurs when subjects modify their behavior in ways that affect the study when they know they are participating in an experiment  A confounding variable is one that influences the dependent or outcome variable but was not separated from the independent variable Disadvantages to Experimental Studies

 ExperimentalObservational Advantages Select subjects and how to assign them to specific groups. Control the independent variable Occurs in natural settings Can be used in situations where experimental would be unethical Disadvantages May occur in unnatural settings Hawthorne effect Confounding variables Cannot show definite cause-effect relationship Expensive and time consuming Inaccuracies So which is better?

  Applying the Concepts  Pg. 16 #1-6 Try it!