Statistics in Behavioral Science Exam 1

Independent Variable

The variable that you manipulate.

What you are interested in.

Dependent Variable

The variable that you measure.

Changes based on the independent variable.

Theory

An explanation for an observation

Hypothesis

A prediction based on a theory

Population Parameter

Numerical summary of the population

Descriptive Statistic

Numerical values that summarize the data collected in the SAMPLE.

Inferential Statistic

Numerical data that lets you infer something about the population.

Inference about the POPULATION using data collected from the sample

Nominal

A variable classified by names or categories

For example, School (AU, BEN, NIU)

Interval

Numbers with no absolute zero (e.g., Temperature)

Ratio

Numbers with an absolute zero (e.g., Distance)

Ordinal

A variable classified by order (e.g., first place, second place, third place)

Random Selection

Everyone in the population has an equal chance of being in the sample.

Random Assignment

Everyone in the sample has an equal chance of being in any of the groups.

Population

The universe

Every single person who is part of a group (All AU students)

Sample

A small, selected group of the population

Empirical

For something to be empirical, it needs to be able to be measured.

Correlation

Relationship

Observational Study

The most basic form of study (e.g., case study, naturalistic observation, survey, etc.)

Correlational Study

A type of study that identifies RELATIONSHIPS between two variables

Quasi-Experimental Study

Similar to an experiment, but is used when you cannot randomly assign the sample to the treatment groups.

Experimental Study

Best type of study!

Can determine cause and effect.

Requires random selection, random assignment, an independent variable, and a dependent variable.

What are the 3 goals of science?

To describe, predict, and explain

What are the measures of central tendency?

Mean, median, and mode

Mean

The average of a data set

Median

The middle number of a data set

Mode

The most frequent number of a data set

What are the measurements of variability?

Range, Variance, and Standard Deviation

What is a percentile rank?

A measure that tells you how many people are at or below your score.

E.g., someone who is in the 90th percentile has a score greater than or equal to 90% of the scores.

What is the difference between positive and negative skew?

1. Positive Skew: The outliers (extremes) are to the right.

2. Negative Skew: The outliers (extremes) are to the left.

What happens to the mean, median, and mode when the distribution is skewed?

The mean changes a lot, the median changes moderately, and the mode changes very little.

All in the direction of the skew.

% of the normal distribution between a Z-score of 0 and 1

34%

% of the normal distribution between a Z-score of 1 and 2

13.5%

% of the normal distribution between a Z-score of 2 and 3

2%

Symmetrical Distribution

A distribution that is the same above and below the mean.

It can be folded on itself.

Probability

The likelihood that something occurs.

Positive Skew

Outliers (extremes) to the right.

Negative Skew

Outliers (extremes) to the left.

Range

The difference between the highest score and the lowest score.