1. Samples, and Populations Chapter 2 Section 2

2. Populations and Samples When conducting a study – must consider what group or groups of people to study How many?

3. Would you vote for there to be a curfew of 10pm for people under 18? Who are you going to ask? How are you going to get an accurate picture? Study a group that represents the target population = whole group you want to study or describe Too costly to survey everyone Study a sample = only a part of the target population

4. Selecting Samples Should be similar as possible to your target population Should use a random sample where individuals are selected by chance from the target population If random sample is big enough, chances are it will accurately represent the whole pop.

5. Selecting Samples, cont’d… Researchers also use a stratified sample – subgroups in the population are represented proportionally in the sample

6. Example: 1000 students in HS Seniors Juniors Sophomores Freshmen 9% 45% 18% 32%

7. How many are you going to actually survey? 32 Seniors 18 Juniors 45 Sophomores 9 Freshmen That’s 10% of the target population in a stratified sample

8. What’s more accurate? Bigger random sample 1,000 to 1,500 people will usually represent the general American population

9. Generalizing Results Sometimes it’s not possible to obtain a random or stratified sample Maybe a researcher is just focusing on one particular group Must be cautious when making generalizations Take in to consideration: Gender Location Socioeconomic background

10. Volunteer Bias Researchers have little control over who responds to surveys Can’t force people to finish survey Must factor in bias – a predisposition to a certain point of view

11. Volunteer Bias, cont’d… Also factor in volunteer bias – these people often have a different outlook from people who do not volunteer for research studies Usually more willing More interested in the research/subject Have more spare time All these factors could skew/slant the results

12. Surveys Great example of volunteer bias Surveys out of Glamour, Seventeen, Motor Trend, Psychology Today. Do these surveys reflect the total population?

13. HOMEWORK!!!! Start thinking about your research question, come up with a hypothesis and how you would go about testing your hypothesis