2. What type of data is it? QualitativeQuantitative Deals with numbers. Data that can be measured. Length, height, area, volume, weight, speed, time, temperature, humidity, sound levels, cost, members, ages, etc. Deals with descriptions. Data can be observed but not measured (counted). Colors, textures, smells, tastes, appearance, beauty, etc. vs.

3. Example: A Painting

4. Univariate Data involving a single variable does not deal with causes or relationships the major purpose of univariate analysis is to describe central tendency - mean, mode, median variability - range, variance, max, min, quartiles, standard deviation. bar graph, histogram, pie chart, line graph, box- and-whisker plot

5. Population vs. Sample Suppose that you were to conduct a study on college students smoking cigarettes. Who would you want to talk to? It would be ideal to interview every student mentioned in the study, the population. It would be very impractical to contact every student, so instead, a statistician will contact a subset of the population, this is called a sample.

6. Bias What does it mean if someone calls you biased? Bias – A sample is biased if it does not accurately reflect the population as a whole. There are many types of bias in statistics.

7. Selection Bias Selection Bias - The way in which we choose people to participate in a survey falls into the category of selection bias. Some examples of selection bias are: –Undercoverage - occurs when some members of the population are inadequately represented in the sample. –Nonresponse bias - occurs when individuals chosen for the sample are unwilling or unable to participate in the survey.

8. Response Bias Response Bias - refers to the bias that results from problems in the measurement process. Some examples of response bias are: –Voluntary response bias - occurs when sample members are self-selected volunteers. –Leading questions - The wording of the question may be loaded in some way to unduly favor one response over another.

9. Let’s discuss! In a 1992 Roper poll conducted for the American Jewish Community of the holocaust, people were asked, “Does it seem possible or does it seem impossible to you that the Nazi extermination of the Jews never happened?” How would you answer the question?

10. The use of double negatives in this question caused confusion in the way people responded to the survey. 22% of those surveyed said that it was possible that the holocaust did not occur. This is an example of a leading question!

11. Fixing the Problem A new survey was conducted in which the question was rephrased, “Does is seem possible to you that the Nazi extermination of the Jews never happened, or do you feel certain that it happened?” In the new survey, only 1% of those surveyed stated that it was possible that the holocaust never occurred.

12. Social Desirability Social desirability - Most people like to present themselves in a favorable light, so they will be reluctant to admit to unsavory attitudes or illegal activities in a survey, particularly if survey results are not confidential.

13. Random Sampling To guard against these biases we use random sampling. Random sampling- a procedure for sampling from a population in which: (a)the selection of a sample unit is based on chance and (b)every element of the population has a known, non-zero probability of being selected.

14. Number of students in a class who turn in a project before it is due Gender of the next baby born at a hospital Amount of fluid ounces dispersed by a soda machine Thickness of the gelatin coating on a pill Birth order (oldest, middle, youngest) of a student Example 1: Quantitative or Qualitative?

15. Example 2: Biased or Unbiased? A uniformed policeman interviews a group of high school students. He asks for the student’s name and then asks if the student has used drugs in the last 30 days. A study on coronary problems was conducted using Duke University students A survey about cafeteria food was conducted by leaving forms at the cash register.

16. Homework: Pick 3 universities that you are interested in. Describe each of these 5 different ways quantitatively and 5 different ways qualitatively This will be collected for a homework grade tomorrow.