# AP Psychology Chapter 2 Part 2

### 23 terms by ZehraAleena Plus

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### Descriptive Statistics

Statistical procedures that organize and summarize, and describe a set of research data.

### Frequency Distribution

A distribution of observed frequencies of occurrence of the values of a variable; indicates how often a particular score or observation occurs.

### Frequency Polygons

Line graphs that displays frequency distributions

### Central Tendency

Mark the center of the distribution. Include mean, median and mode.

### Mean

Average of all the scores in the distribution. Most commonly used measure of central tendency, although accuracy can be distorted by extreme scores.

### Median

Central score of the distribution.

### Mode

Score that appears most frequently.

### Outliers (Extreme Scores)

Extremely high or low values in a set of data that can affect the mean and skew distributions.

### Positively Skewed

When a distribution includes extreme scores that are very high. Contain more low scores than high scores; the skew is produced by the unusually high score. Curve at left, tail on right.

### Negatively Skewed

When a distribution includes extreme scores that are unusually low and the low scores skew the distribution. Contain a higher number of high scores than low scores. Curve at right, tail on left.

### Range

Distance between the highest and lowest score in a distribution

### Variance

Measures the degree of dispersion or scatter. Standard deviation squared.

### Standard Deviation

Measures average distance of any score in the distribution from the mean. The higher it is, the more spread out the distribution.

### Z-Scores

Measure the distance of a score from the mean in units of standard deviation. Scores below the mean are negative and scores above the mean are positive.

### Normal Curve (bell curve)

Frequency distribution in which most measurements are centered around the mean and the two sides of the distribution are symmetrical. Theoretical bell-shaped curve for which the area under the curve lying between any two z-scores has been predetermined. 68% of scores fall within one standard deviation, 95% within two standard deviations. and 99% within three.

### Correlation

Measures the relationship between two variables. Positive=presence of one predicts the presence of the other. Negative=presence of one predicts absence of the other. No relationship=none exists.

### Correlation Coefficient

Measures the strength of a correlation. -1 is a perfect negative and +1 is a perfect positive. 0 denotes weakest.

### Scatter Plot

Graphs pair of values. Useful for correlations.

### Line of Best Fit (Regression Line)

Line drawn through the scatter plot that minimizes the distance of all the points from the line. Upward slope=positive correlation. Downward slope=negative.

### Inferential Statistics

Determines whether or not the findings of the study can be applied to the larger population.

### Sample Error

The extent to which the sample differs from the population

### P Value

The probability level which is used to decide if results are statistically significant (not due to chance); The smaller the value, the more statistically significant.

### Statistically Significant Results

A p-value of .05, meaning there is a 5% chance of the results occurring by chance.

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