Psych Stats Test 1

What is a population?

The entire group of individuals or scores that a researcher is interested in studying.

What is a sample?

A subset of a population that is actually studied.

Why do researchers use samples?

Usually because studying an entire population is impractical or impossible.

What is random sampling?

A sampling method in which members of the population have a known/chance opportunity to be selected.

What is a parameter?

A numerical characteristic of a population.

What is a statistic?

A numerical characteristic calculated from a sample.

What are the four levels of measurement?

Nominal

What is nominal measurement?

Categories or names with no meaningful order.

What is ordinal measurement?

Categories that can be meaningfully ordered or ranked

What is interval measurement?

Ordered values with equal intervals

What is ratio measurement?

Ordered values with equal intervals and a true/absolute zero.

What is the shortcut for identifying levels of measurement?

Categories → order → equal intervals → true zero.

What level is a person's major?

Nominal; majors are categories without meaningful ranking.

What level is a letter grade?

Ordinal; grades have a meaningful order but unequal/unknown intervals.

What level is class rank?

Ordinal; ranks have order but differences between ranks are not equal intervals.

What level is a 1–5 satisfaction rating?

Ordinal; responses are ordered but equal intervals cannot be assumed.

What level is temperature in Fahrenheit?

Interval; intervals are equal but 0°F is not a true zero.

What level is temperature in Celsius?

Interval; intervals are equal but 0°C is not a true zero.

What level is height in inches?

Ratio; equal intervals exist and 0 inches represents no height.

What level is weight?

Ratio; equal intervals exist and zero represents the absence of weight.

What level is number of siblings?

Ratio; zero means no siblings and the intervals are equal.

What level is number of times someone cheats?

Ratio; zero means none and the values have equal intervals.

What level is eye color?

Nominal; eye colors are categories without meaningful order.

What level is a pain rating from 1–10?

Ordinal; the ratings have order but equal intervals cannot be assumed.

What is a simple frequency table?

A table that organizes individual scores or categories with their frequencies.

What is a grouped frequency table?

A table that combines scores into class intervals and gives the frequency in each interval.

What is frequency?

The number of cases or scores falling in a category or class interval.

What is relative frequency?

The percentage of cases in a category or class interval: (frequency/N) × 100.

What is cumulative frequency?

The number of cases at or below a given class interval.

What is cumulative relative frequency?

The percentage of cases at or below a given class interval.

How do you calculate cumulative frequency?

Start at the bottom and add frequencies upward.

How do you calculate cumulative relative frequency?

Start at the bottom and add relative frequencies upward.

What should cumulative relative frequency total?

100% at the highest interval.

What should cumulative frequency total?

N

What must class intervals be?

Exhaustive

What does mutually exclusive mean?

Each score can fit into only one class interval.

What does exhaustive mean?

Every possible score has a place in one of the intervals.

What does continuous mean for class intervals?

There are no gaps between possible score values.

How many grouped class intervals should there usually be?

Between 5 and 15.

How do you find the number of scores covered by a range?

Highest score − lowest score + 1.

What do you do if the range does not divide evenly by 5–15?

Adjust the upper or lower limit to a possible value rather than simply rounding.

What should you NOT do when choosing grouped intervals?

Do not simply round the number of intervals to force a fit.

Where should high scores appear in a frequency table?

At the top.

What is a frequency histogram?

A graph using bars to display frequencies across continuous class intervals.

What goes on the horizontal axis of a histogram?

The class intervals or scores.

What goes on the vertical axis of a histogram?

Frequency.

What should the axes of a histogram show?

Clear labels

Where should the axes intersect?

At 0

What should histogram class intervals be?

Exhaustive

What is an advantage of a histogram?

It is familiar

What is a disadvantage of a histogram?

It does not clearly show median/quartiles

What is a frequency polygon?

A graph created by connecting the frequencies of intervals with a continuous line.

What is an advantage of a frequency polygon?

It makes the overall shape of a distribution easy to see and compare.

What does symmetry mean in a distribution?

The left and right sides have approximately the same shape.

What does skew mean?

A distribution is asymmetric because one tail extends farther than the other.

What is right skew?

A distribution with a longer tail toward higher scores.

What is left skew?

A distribution with a longer tail toward lower scores.

What does unimodal mean?

The distribution has one mode or peak.

What does bimodal mean?

The distribution has two modes or peaks.

What does trimodal mean?

The distribution has three modes or peaks.

What does multimodal mean?

The distribution has multiple modes or peaks.

What is a box-and-whiskers plot?

A graph showing the median

What is an advantage of a boxplot?

It clearly identifies outliers

What is a disadvantage of a boxplot?

It does not show exact individual values or frequencies clearly.

What does the middle line in a boxplot represent?

The median or 50th percentile.

What does the bottom of the box represent?

The 25th percentile or first quartile.

What does the top of the box represent?

The 75th percentile or third quartile.

What are outliers on a boxplot?

Values shown separately from the main whiskers.

What is a stem-and-leaf plot?

A display that organizes exact scores by separating each score into a stem and leaf.

What is an advantage of a stem-and-leaf plot?

It preserves exact values while showing shape

What is a disadvantage of a stem-and-leaf plot?

It can be unfamiliar and sometimes difficult to interpret.

What does N represent?

The total number of cases or scores in the distribution.

What is the mean?

The arithmetic average of all scores.

What is the population mean symbol?

μ.

What is the sample mean symbol?

M or x̄

What is the basic mean formula?

Mean = sum of scores ÷ number of scores.

What does the mean take into account?

Every score in the distribution.

What is a major weakness of the mean?

It is sensitive to extreme scores

When can the median be better than the mean?

When extreme scores or skew make the mean misleading.

What is the median?

The 50th percentile; the point with half the scores above and half below.

How does the professor find the median case when N is odd?

Order scores highest-to-lowest and use (N + 1) ÷ 2.

What happens when N is even when finding the median?

Average the two middle scores.

What is an advantage of the median?

It is less affected by extreme scores

What is a disadvantage of the median?

It does not use every score and cannot be incorporated into later analyses.

What is the mode?

The most frequently occurring score or category.

What is an advantage of the mode?

It is least affected by extreme scores

What is a disadvantage of the mode?

There can be multiple modes and it cannot be incorporated into later analyses.

Which central tendency measure can be used with nominal data?

Mode.

When does mean = median = mode?

In a symmetric distribution with the typical single central peak.

What relationship suggests right skew?

Mean > median > mode.

What relationship suggests left skew?

Mean < median < mode.

Why can the mean be misleading in a skewed distribution?

Extreme values pull the mean toward the long tail.

What is variability?

The amount of spread or dispersion among scores.

What is the range?

The highest score minus the lowest score.

What is a major weakness of the range?

It uses only two scores and is strongly affected by extreme values.

What is population variance?

The average squared deviation from the population mean

What is sample variance?

The sample estimate of variance

What is population standard deviation?

The standard deviation of a population

What is sample standard deviation?

The standard deviation of a sample

What does standard deviation describe?

The typical amount scores deviate from the mean.