1. Analysis…Measures of Central Tendency How can we make SENSE of our research data???

2. Describing Data A meaningful description of data is important in research. Misrepresentation may lead to incorrect conclusions.

3. Statistical Reasoning in Everyday Life Doubt big, round, undocumented numbers as they can be misleading and before long, become public misinformation. Apply simple statistical reasoning in everyday life to think smarter!

4. Comparison Below is a comparison of different research methods.

5. Statistical Reasoning Statistical procedures analyze and interpret data allowing us to see what the unaided eye misses. Composition of ethnicity in urban locales

6. Normal Distribution Normal distributions form a bell-shaped or symmetrical curve. A symmetrical, bell-shaped curve that describes the distribution of many types of data (normal distribution). Most scores fall near the mean. In a normal distribution of test scores, the percentage of scores that fall at or above the mean score is 50. The percentage of test scores that fall at or below the mean score is also 50.

7. Figure 1.10 The normal curve Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers

8. Measures of Variation Range: The difference between the highest and lowest scores in a distribution. Standard Deviation: A computed measure of how much scores vary around the mean.

9. Table 1.4 Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers

10. Con’t. Approx. 1/3 of the scores fall one standard deviation below the mean and 1/3 of the scores fall one standard deviation above the mean. –Example: The Wechsler IQ tests have a mean of 100 and a standard deviation of 15. –This means that 1/3 of the people taking these tests will have scores between 85 and 100 and another 1/3 will have scores between 100 and 115.

11. More… All score-based normal curves have the following 68-95-99.7 rule in common. –Approx. 68% of all scores fall within one standard deviation of the mean. –Approx. 95% of all scores fall within two standard deviations of the mean. –Approx. 99.7% of all scores fall within three standard deviations of the mean.

12. What can “skew” a normal distrbutition? Positively Skewed Distributions: –Contains a preponderance of scores on the low end of the scale. –The mean will be higher than the median in this kind of distribution. –Because of this, the median is a better representation of central tendency.

13. Another… Negatively Skewed Distributions: –Contains a preponderance of scores on the high end of the scale. –The mean will be lower than the median in a negatively skewed distribution. –Because of this, the median is a better representation of central tendency too!

14. How to tell the difference… Remember that a positively skewed curve… –Looks like a “P” lying on its back. The preponderance of scores are to the left or the low end of the scale.

15. Figure 1.9 A Skewed Distribution Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers

16. Illusion of Control 1.Illusory Correlation: the perception of a relationship where no relationship actually exists. 2.Regression Toward the Mean: the tendency for extremes of unusual scores or events to regress toward the average. That chance events are subject to personal control is an illusion of control fed by:

17. Making Inferences A statistical statement of how frequently an obtained result occurred by experimental manipulation or by chance.

18. Making Inferences 1.Representative samples are better than biased samples. 2.Most experiments are conducted with a small sample of subjects. 3.Less-variable observations are more reliable than more variable ones. 4.More cases are better than fewer cases. When is an Observed Difference Reliable?

19. Making Inferences: Other Key Points Psychologists want to generalize the results from their small sample to a larger population. Inferential statistics are used to determine how likely it is that a study’s outcome is due to chance and whether the outcome can be legitimately generalized to the larger population from which the sample was selected.

20. Making Inferences When sample averages are reliable and the difference between them is relatively large, we say the difference has statistical significance. It is probably not due to chance variation. For psychologists this difference is measured and set at 5 percent.(Considered “statistically significant”) When is a Difference Significant?

21. Significance Con’t. The smaller the difference, the better chance that the results did NOT occur by chance.

22. Frequently Asked Questions About Psychology Q. Can laboratory experiments illuminate everyday life? Ans: Artificial laboratory conditions are created to study behavior in simplistic terms. The goal is to find underlying principles that govern behavior.

23. FAQ Q. Does behavior depend on one’s culture and gender? Ans: Even when specific attitudes and behaviors vary across cultures, as they often do, the underlying processes are much the same. Biology determines our sex, and culture further bends the genders. However, in many ways woman and man are similarly human. Ami Vitale/ Getty Images

24. FAQ Q. Is psychology free of value judgments? Ans: No. Psychology emerges from people who subscribe to a set of values and judgments. © Roger Shepard

25. FAQ Q. Is psychology potentially dangerous? Ans: It can be, but is not when practiced responsibly. The purpose of psychology is to help humanity with problems such as war, hunger, prejudice, crime, family dysfunction, etc.

26. FAQ Q. Is it ethical to experiment on people? Ans: Yes. Experiments that do not involve any kind of physical or psychological harm beyond normal levels encountered in daily life may be carried out.

27. FAQ Q. Why do psychologists study animals, and is it ethical to experiment on animals? Ans: Studying animals gives us the understanding of many behaviors that may have common biology across animals and humans. From animal studies, we have gained insights to devastating and fatal diseases. All researchers who deal with animal research are required to follow ethical guidelines in caring for these animals. D. Shapiro, © Wildlife Conservation Society