Research Modules 2: Typical and Extreme Scores

Probability

For a situation with multiple possible outcomes, the probability of a specific outcome is a fraction or proportion of all possible outcomes.

Random Sampling

Each individual in the population has an equal chance of being selected.

Simple Random Sample

A sample obtained through random sampling where each individual has an equal chance of selection.

Independent Random Sampling

Each individual has an equal chance of being selected, and the probability of selection remains constant if multiple individuals are chosen.

Sampling with Replacement

Returning each individual to the population before the next selection to maintain constant probabilities.

Central Tendency

A feature describing the center of a data distribution.

Variability

A feature describing the spread or dispersion of data in a distribution.

Histogram

A graphical representation of a data distribution.

Normal Shape

Data distribution where the majority of data is in the middle, with relatively fewer values at the extremes.

Normal Distribution

A distribution where most observations are in the middle, symmetrical, and decrease in frequency towards the tails.

Extreme Scores

Scores at the edges of a distribution, occurring infrequently and differing significantly from typical scores.

2s Rule of Thumb

In a normally shaped distribution, approximately 95% of scores fall within 2 standard deviations of the mean.

2s Rule of Thumb: Typical Scores

Scores within 2 standard deviations of the mean, expected and frequent in the distribution.

2s Rule of Thumb: Extreme Scores

Scores outside 2 standard deviations of the mean, infrequent and not expected in the distribution.

Applying 2 Rule of Thumb

Double standard deviation then add and subtract that number from the mean to define the critical limits to determine what is typical and what is extreme