PSY 210 Final Study Guide
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What is statistics?
Value that describes a sample

What is population?
Set of all inividuals of interest in a particular study

What is sample?
Set of individuals selected from a population, usually inteded to represent the population in a research study

What is parameter?
A value that describes a population

Independent variable vs. dependent variable
 Independent variable: the variable being manipulated by the researcher
 Dependent variable: the one that is observed to assesss the effect of the treatment






Shape of Distribution
Positively skewed

Shape of Distribution
Negatively skewed



Measures of Central Tendency: Mode
The score or category has the greatest frequency

Measures of Central Tendency: Median
The score that divides the distibution in half

Measures of Central Tendency: Mean
Arithmetic average

Which Measure of Central Tendency is most influenced by outliers?
 Mean
 Incorporate every score

Variance Equation
variance = mean squared deviation =
 sum of squared deviations
 number of scores


Population Standard Deviation

Sample Standard Deviation



What causes variance to go up?

What causes variances to go down?

How to determine probability of zscore
Base probability percentage with zscore of normal distribution
 Example:
 Given:

 What percent scored higher than you on a test?
 P(z>+1.00)=.1587 (15.87%)

How to find a zscore with that probability
Example: For a normal distribution, what zscore separated the top 10% from the rest of the distribution?
 Z=+1.28


Standard Error vs. Standard Deviation




#38 on Test: On average, what value is expected for the Fratio if your null hypothesis is true?

Correlation
A statistical technique that is used to measure and describe a relationship between two variables
NO manipulation of variables, just looking if 2 variable have a relationship to each other

Positive correlation
2 variables that you are comparing move in the same direction

Negative correlation
2 variables that you are comparing move in opposite directions

Parametric test
 Inferences about population from statistics that you calculated
 Test hypotheses about population parameters
 Require a numerical score for each individual
 Require data measured on an intercal or ratio scale

Nonparametric Tests
 Do not make statements about relationships to population parameters
 Data can be measured on nominal or ordinal scales
 Require fewer assumptions
 Are less sensitive than parametic tests