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Perceiving Order in Random Events

-Given some random data, we look for order or patterns. We typically find patterns, because

random sequences often dont look random.

-Given enough random events, something weird will happen.

III. Experimentation:

Exploring Cause and Effect

-Experiment: a research method in which an investigator manipulates one or more factors

(independent variable) to observe the effect on some behavior or mental process (dependent

variable). By random assignment of participants, the experimenter aims to control other relevant

factors.

-If a behavior changes when we vary an experimental factor, then we know the factor is having

an effect.

-Instead of showing naturally occurring relationships, an experiment manipulates a afactor to

determine its effect.

Evaluating Therapies

-In drug studies, the participants are blind(uninformed) about what treatment, if any they are

getting. One group gets the actual treatment, while the other gets aplacebo (such as a pill with

no drug in it).

-Double blind procedure: an experimental procedure in which both the research participants are

ignorant (blind) about whether the research participants have received the treatment or a placebo.

-Placebo effect: experimental results caused by expectations alone; any effect on behavior caused

by the administration of an inert substance or condition which is assumed to be an active agent.

-Experimental condition: the condition of an experiment that exposes participants to the

treatment, that is, to one version of the independent variable.

-Control condition: the condition of an experiment that contrasts with the experimental condition

and serves as a comparison for evaluating the effect of the treatment.

-Random assignment: assigning participants to experimental and control conditions by chance,

thus minimizing preexisting differences between those assigned to the different groups. Random

assignment roughly equalized the 2 groups in age, attitudes, and every other characteristic.

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Independent and Dependent Variables

-Independent variable: the experimental factor that is being manipulated; the variable whose

effect is being studied.

-Dependent variable: the outcome factor; the variable that may change in response tomanipulations of the independent variable.

-Experiments aim to manipulate an independentvariable, measure the dependentvariable, and

control all other variables.

IV. Statistical Reasoning

Describing Data

-One way to organize data is by using a bar graph. When reading statistical graphs, you need to

be careful. People can design a graph to make a difference look smaller or bigger.

Measures of Central Tendency

-You also need to use measures of central tendency, a single number that represents a whole set

of numbers.

-Mode: the most frequently occurring score(s)

-Mean: the arithmetic average of a distribution

-Median: the middle score in a distribution

-Data can become skewed, or lopsided, when the mean is influenced by a few extreme scores.

Measures of Variation

-It is important to know the amount ofvariation in the data; how similar or diverse the scores

are.

-Averages from scores with low variability are more reliable than scores with high variability.

-Range: the difference between the highest and lowest score in a distribution.

-Standard deviation: a computes measure of how much scores vary around the mean score.

Making Inferences

When is an Observed Difference Reliable?

1. Representative samples are better than biased samples. Remember what population astudy has sampled.

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2. Less-variable observations are more reliable than those that are more variable.3. More Cases are better than fewer.

When is a Difference Significant?

-Statistical significance: a statistical statement of how likely it is that an obtained result occurredby chance.

-Psychologists dont make much of a finding unless the odds of its occurring by chance are less

than 5%

-Statistical significance indicates thepossibility that a result will happen by chance. It is not an

indication of how important the result is.