DO NOW:

• Hole punch your new DO NOW sheets.

• Organize your binders!• Answer on your DO NOW sheet:

What is an illusory correlation?

Variables and Statistics

AP PsychologyMs. Desgrosellier

10.5.2009

Objectives:

• SWBAT explain the difference between an independent and a dependent variable.

• SWBAT explain the importance of statistical principles, and give an example of their use in everyday life.

• SWBAT how bar graphs can misrepresent data.

Independent and Dependent Variables

• Variable: anything that can vary in an experiment

• IV: the experimental factor that is manipulated; the variable whose effect is being studied.• You can have more than one in an

experiment!

Independent and Dependent Variables

• DV: the outcome factor; the variable that may change in response to manipulations of the independent variable.

• Both require operational definitions

Summary

• Experiments aim to manipulate an independent variable

• Measure the dependent variable• Control all other variables (age, gender,

etc.)• Two conditions in an experiment:

experimental condition and a comparison condition

• Random assignment: equates the conditions before any treatment effects happen

Comparing Research Methods

Examples

• Read the following scenario. Identify the independent and dependent variables. Was random assignment used?

Examples

• Researchers are studying how cocaine affects cognitive processing in rats. Rats are randomly put into two groups: One group of rats receives a minimal dose of cocaine each day. The other group does not receive any cocaine. The rats are then put in a maze and are timed to see how long it takes them to reach the food in the center of the maze.

Examples• Researchers want to study how people see

colors affects memory. There are three groups. One group of all men is shown a normal colored picture. One group of all women is shown the same picture, but all the red tones are missing. A third group of both men and women is shown the same picture, but all the normal colors have been replaced with their natural opposite. Participants are then asked to describe the picture in great detail. The number of objects in the picture that are accurately recalled are counted.

Statistical Reasoning

• Statistics are tools that help us see and interpret what the unaided eye might miss by organizing, summarizing, and making inferences from data.

• Random estimates often misread reality and can then mislead the public

Statistical Reasoning

• Examples:• We use only 10% of our brains. Or is it

closer to 90%? Different studies have said both.

• 10% of people are gay or lesbian. Or is it 2-3%, like some national surveys have found?

Statistical Reasoning

• Remember: doubt big, round, undocumented numbers.

• Focus on thinking smarter by applying simple statistical principles to everyday reasoning.• Ask yourself: what is the sample size? Was

it representative? Did researchers use random assignment/control for extra variables? How was the data analyzed?

Describing Data

• First thing’s first: researchers must describe their data

• A common, simple way: the bar graph• People can design a graph to make a

difference look small or big, depending on what they want to emphasize

• Be critical when you look at figures in magazines, newspapers, or on TV: read the labels and note their range

Describing Data

Homework

• Read pgs. 42 – 44• STUDY for your Unit 2 exam

(Friday)• See Ms. Desgrosellier with any

questions or for make-up work!