1. Psy B07 Chapter 1Slide 1 BASIC CONCEPTS

2. Psy B07 Chapter 1Slide 2  Population  Random Sampling  Random Assignment  Variables  What do we do with the data? Outline

3. Psy B07 Chapter 1Slide 3 Population  The entire collection of events that you are interested in.  Although we wish to make claims about the entire population, it is often too large to deal with.  There are two ways of getting around this....

4. Psy B07 Chapter 1Slide 4 Random Sampling  Choose a subset of the population ensuring that each member of the population has an equivalent chance of being sampled.  Examine that sample and use your observations to draw inferences about the population.  Example : Voting polls, television ratings

5. Psy B07 Chapter 1Slide 5 Random Sampling  Note, however, that the inferences drawn are only as good as the randomness of the sample.  If the sample is not random, it may not be representative of the population. When a sample is not representative of its parent population, the external validity of any inferences is called into question.  Example : Most psychology experiments

6. Psy B07 Chapter 1Slide 6 Random Assignment  When studying the effects of some treatment variable, it is also important to randomly assign subjects to treatments.  Random assignment reduces the likelihood that groups differ in some critical way other than the treatment.

7. Psy B07 Chapter 1Slide 7 Random Assignment  If random assignment is not used then the internal validity of the experimental results may be compromised

8. Psy B07 Chapter 1Slide 8 Variables  Assume we have a random sample of subjects that we have randomly assigned to treatment groups.  Example: stop-smoking study

9. Psy B07 Chapter 1Slide 9 Variables  Now we must select the variables we wish to study, with the term variable referring to a property of an object or even that can take on different values.  Example: # of cigs smoked, abstinence after one week.  Note the distinction; # of cigarettes smoked is a continuous variable, whereas abstinence is a categorical variable.

10. Psy B07 Chapter 1Slide 10 Variables  Another distinction related to variables concerns variables we measure (dependent variables) versus variables we manipulate (independent variables).  For Example: Whether or not we give a subject the stop-smoking treatment would be the independent variable, and the # of cigarettes smoked would be a dependent variable.

11. Psy B07 Chapter 1Slide 11 What do we do with the data?  Descriptive Statistics are used to describe the data set.  Examples: graphing, calculating, averages, looking for extreme scores.

12. Psy B07 Chapter 1Slide 12 What do we do with the data?  Inferential Statistics allow you to infer something about the parameters of the population based on the statistics of the sample, and the various tests we perform on the sample.  Examples: Chi-Square, T-Tests, Correlations, ANOVA  NOTE: See sections in book on measurement scales.