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Statistics
The branch of applied mathematics that researchers use to organize, describe, and draw conclusions about the quantitative results of their studies

Descriptive statistics
 Statistics used to organize, summarize, and describe data
 Includes measures of central tendency, variability, and relationships

Measures of central tendency
 a measure or score that describes the center, or middle, of a distribution or scores
 Mean � the arithmetic average of a group of scores
 Median � the middle score or value when scores are arranged from highest to lowest
 Mode � the score that occurs most frequently in a group of scores

Histogram
A bar graph that depicts the number of scores within each class interval in a frequency distribution

Variability
How much the scores in a distribution spread out away from the mean

Range
The difference between the highest score and the lowest score in a distribution of scores

Standard deviation
A descriptive statistic reflecting the average amount that scores in a distribution deviate, or vary, from their mean

Normal curve
 A symmetrical bellshaped frequency distribution that represents how scores are normally distributed in a population
 Most scores fall near the mean, and fewer and fewer scores occur in the extremes above or below the mean
 68% of scores in a normal distribution fall within 1 standard deviation of the mean (34.13% above and 34.13% below)
 Almost 95.5% of scores deviations above and
 99.72% fall between above and below

The Correlation Coefficient
A numerical value indicating the strength and direction of a relationship between two variable

Positive correlation
A relationship between two variable in which both vary in the same direction

Negative correlation
A relationship between two variable in which an increase in one variable is associated with a decrease in the other variable

Inferential Statistics
 Statistical procedures based on probabilities that allow researchers to make inferences about the characteristics of the larger population from observations and measurements of a sample
 Estimates are derived of how much confidence can be placed in those inferences

Population
The entire group of interest to researchers and to which they wish to generalize their findings; the group from which a sample is selected

Sample
The portion of any population that is selected for study and from which generalizations are made about the entire population

Tests of statistical significance
 Statistical tests that estimate the probability that a particular research result could have occurred by chance
 The estimates derived from tests are stated as probabilities
 A probability of .05 means that the experimental results would be expected to occur by chance no more than 5 times out of 100
 The .05 level is usually required as a minimum for researchers to conclude their findings are statistically significant

Replication
The process of repeating a study with different participants and preferably a different investigator to verify research

