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# Descriptive Statistics

Descriptive statistics tell us features of a data set, such as its mean, median, mode or standard deviation.

What Are the First and Third Quartiles?
The process of finding the median of a set of data can be continued to split the data into four pieces. These pieces are separated by numbers known as quartiles.

Time Series Graphs
Time series graphs display paired data in which one coordinate of each pair is a time measurement. A time series graph shows how the measurement of a varaible changes over time.

What Is a Percentile?
Percentiles, not to be confused with percents, give a way to compare an ordered list of data to itself based upon the percentage of the data below it.

What Is Skewness?
Not all distributions are symmetric. Those that are asymmetric have different degrees of asymmetry and are said to be skewed.

What is a Five Number Summary
A five number summary combines five descriptive statistics of minimum, first quartile, median, third quartile and maximum to give us a fuller picture than what we might have by just looking at one of these numbers.

What Are Moments in Statistics
Moments of a data set are calculated b

What Is Kurtosis?
When looking at the shape of a distribution of data, rather than considering the number of peaks or how spread out the data is, we can consider the shape of the peaks.

Range Rule for Standard Deviation
The standard deviation can be an involved statistic to calculate. If we only need a rough estimate, then there is a very simple formula - only involving two arithmetic operations - that can be used to calculate an estimate of the standard deviation.

Empirical Relationship Between the Mean, Median and Mode
The mean, median and mode all measure the center of a set of data, however they do so in different ways. Although there is no guarantee that these three numbers will be related to one another, there is an interesting emperical relationship between these three descriptive statistics.

What Is the Range in Statistics
The range is a descriptive statistic that gives a very crude indication of how spread out a set of data is.

Differences in Descriptive and Inferential Statistics
Statistics has two main areas, known as descriptive statistics and inferential statistics. Although these areas use the same procedures, there are a number of differences between them.

What Is the Interquartile Range Rule?
It helps to have a systematic way to look for outliers. One easy way to do this is to use the interquartile range rule. We use two of the numbers from a five number summary to help us determine if we have a potential outlier.

How to Construct a Histogram
Histograms are used extensively in statistics. Learn how to construct a histogram by hand.

Frequencies and Relative Frequencies
In the construction of a histogram we have an option of using frequencies or relative frequencies for the heights of the bars

What Is the Trimean?
The trimean is a measurement of central tendency that is not as well known as the median, mode or mean. The trimean is easily calculated with the use of the median, first quartile and third quartile.

What Is the Midhinge?
The midhinge is a measure of position that uses the first and third quartiles. This number is helpful in the calculation of other descriptive statistics, such as the trimean.

Slope of Regression Line and Correlation Coefficient
The correlation coefficient r indicates the straight line relationship of a set of paired data. The slope of this straight line is directly dependent on the value of r.

How to Calculate the Correlation Coefficient
The correlation coefficent provides a measurement for how well a straight-line fits a set of paired data. See how this number is calculated through the use of sample standard deviations.

What Is a Least Squares Line
The least squares line is the unique line that passes through the midst of a set of paired data in such a way that the distances from the points to the lines are minimized. Find out how precisely this is done.

What Are the Maximum and Minimum?
The minimum and maximum are two very basic descriptive statistics. These numbers tell us the smallest and largest values in our data set, but are used for other things in statistics.

What Is a Two-Way Table?
When dealing with two categorical variables, a two-way table is a helpful way to display this data. Find out what is a two-way table.

How Do We Determine What Is an Outlier?
The determination of what constitutes an outlier can sometimes seem to be quite subjective. It is important to have an objective measurement of this phenomenon in statistics.