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Dependent Variable

Definition: The variable that is measured.

Example: Mate Choice

Application: This study explains how taking birth control can affect people's mating choices. Since mating choice is the variable that is being measured, we can conclude that it is the dependent variable.

Nominal Variable

Definition: mutually exclusive and exhaustive categories differing in some qualitative aspect.

Example: Milk

Application: This article explains the pro's and con's of different types of milk: cow's, goat's, soy, almond, rice and hemp. The different type of milk is the nominal variable because it is a mutually exclusive category that shows the different types.

Ordinal Variable

Definition: the categories must still be mutually exclusive and exhaustive, but in addition they must also indicate the order of magnitude of some variable.

Example: National Parks

Application: This article shows the most visited national parks in the U.S. The category in this article is mutually exclusive and it is ranked in order of most visited. Thus, the ordinal value in this article is "most visited rank", since it places the national parks in order of magnitude.

Interval Variable

Definition: has all the properties of an ordinal scale, and a given distance between measures has the same meaning anywhere on the scale.

Example: Twitter

Application: The graph titled, Tweets per Hour describes the amounts of tweets received per hour. It's measurement scale has an equal distance of 5 hours thus making it an interval variable.

Ratio Variable

Definition: has all the properties of an interval scale plus an absolute zero point.

Example: C60 Melting

Application: This video shows the outcome of melting a C60 cluster, it is using a Kelvin scale to measure degrees. Kelvin temperature scale is an example of ratio variable since it has an absolute zero, meaning that there can not be negative degrees kelvin. The distance between degrees is equal.

Frequency Distribution (regular, grouped, relative, or cummulative)

Definition: shows the number of observations for the possible categories or score values in a set or data.

Example:United States Crime Rate

Application: The crime index table is an example of a frequency distribution because it shows the total number of crimes observed.

Percentile (percentile or percentile rank)

Definition: a percentile rank is the percentage of cases in a distribution that falls below a given point on the measurement scale.

Example: SAT Scores: Males and Females

Application: The chart is an example of percentile rank since it shows the number of males and females with a certain score and its rank. For instance 125 females got a score of 2400 and according to the chart, the percentile rank for those 125 females is 99.


Definition: a graph that consists of a series of rectangles, the heights of which represent frequency or relative frequency.

Example: Kiwi Poll Guy

Application: The chart's titled Number of Seats is an example of a histogram, it depicts the number of seats won by each party.

Frequency Polygon

Definition: a graph that consists of connected dots above the midpoint of each possible class interval (height of the dots corresponds to frequency or relative frequency).

Example: America by the Numbers: Who We Are (Slide 4)

Application: Slide 4 of the multimedia article is an example of a frequency polygon.

Bar Diagram

Definition: used for qualitative data, a graph that is similar to a histogram, except that space appears between the rectangles.

Example: Mexico's Drug War

Application: The bar diagram in this article illustrates the number of deaths per week caused by Mexico's drug wars.

Pie Chart

Definition: used for qualitative data, area in any piece of the pie shows the relative frequency of a category.

Example: Violence Against Women

Application: The pie chart (Graph 8) illustrates the age of the female victims by percentages.


Definition: The sum of all the scores divided by the total number of scores.

Example: Hank Aaron

Application: the sum of Aaron's PA or plate appearances is 13940 if you divide the total sum by the total number of scores, which is then Aaron's mean PA appearance equals 606.09


Definition: The value that divides the distribution into halves, another name for P50.

Example: National Hourly Wage

Application: The variables are ranked by the median hourly wage. For example, the median hourly wage of Arby's is $8.33/hour while the median hourly wage of KFC is $7.82/hour.


Definition: The score that appears with the greatest frequency.

Example: Hank Aaron

Application: the mode of Hank Aaron's runs scores is 103 since it is the number with the greatest frequency.


Definition: the difference between the lowest score and the highest score.

Example: STD Statistics

Application: The second chart shows the estimated number of new cases of chlamydia worldwide from the year 1995 and 1999. To find the range of the new cases found in the year 1995, we take total highest total number of cases 40.48 and subtract by the lowest total number of cases 0.30, which equals 40.18. Thus the range of the estimated number of new cases of chlamydia is 40.18.


Definition: The mean of the squares of the deviation scores, or the average squared deviation from the mean.

Example: Batting Practice

Application: This article states that the variance of Aaron's total home runs equals 119.62.

Standard Deviation

Definition: The square root of the variance.

Example: Poverty and Birth Rates

Application: This study relates birth rates and poverty in California. The first chart shows an example of standard deviation for each category listed.

Standard Scores (z-scores)

Definition: States how far away a score is from the mean in standard deviation units; one type of standard score.

Example: Ziggie's Z Score

Application: Ziggie wants to join the Navy Seals but needs a test score ranked in the 1% to qualify. His test results reveal that he got a total score of 53, a mean of 50, and a standard deviation of 10. The video gives an example of how to calculate the z score, we take 53 and subtract by 50 then divide by 10, this results in a z score of .3. The results show that Ziggie did not make the top 1 percent and thus did not qualify to join the navy seals.


Definition: A graph of a bivariate distribution consisting of dots at the point of intersection of paired scores.

Example: Finance and Growth

Application: Figure 4 is a depiction of a scatterplot measuring commercial central banks and growth.

Correlation (r)

Definition: a measure of the degree of relationship between two variables.

Example: Music

Application: This study shows the measure between music and intelligence. The researcher used SAT scores to measure intelligence. The results show that those who listen to Beethoven ranked highest in intelligence, while those who listen to artists such as Lil Wayne and Beyonce are ranked among the lowest intelligence.

EXTRA CREDIT: Correlation does not equal causation

Definition: The fact that X and Y vary together is a necessary but not sufficient condition for use to conclude that there is a cause-and-effect connection between them. In other words, a correlation between two variables does not equal causation since there can be other possibilities that can affecting the variables.

Example: Wine

Application: The article explains that there is very little correlation between price of wine and taste quality. The tasters included a broad range of individuals from wine experts to everyday wine drinkers. The results showed that the correlation was negative, meaning that individuals did not prefer the taste of expensive wines over cheaper wines. However, in the studies that involved wine experts only, there was a slight positive correlation but not sufficient enough. The article also explains why people still prefer expensive wine even though there is a negative correlation. For instance, the subjects could be influenced by the "wine placebo effect" which means that knowing that a wine is expensive can influence taste.

EXTRA CREDIT: Critically Evaluating Research

Guideline 7: Check that results are fairly represented in graphics or concluding statements.

Example: Gas Loan

Application: The chart (29 seconds into the clip), is supposed to represent the gas prices by year. However, the data is misrepresented in the graph, the variables of the horizontal axis are too small to depict and the two female drawings on the vertical axis are distracting.

Guideline 2: Consider the Source

Example: Mac vs. PC

Application: This commercial is arguing that Mac home movie results are better than the PC. However, when viewing a commercial like this one must take the source into consideration. Since the commercial is done by Mac one can conclude that the argument is biased.

◄ Back to Descriptive Statistics PSY 202 Fall 2009 page

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