Glossary of Biostats Chapter Two

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frequency distribution
lists data calues (either individually or by groups of intervals), along with their corresponding frequencies (or counts)
lower class limits
smallest numbers that can belong to the different classes
upper class limits
largest numbers that belong to the different classes
class boundaries
numbers used to seperate classes, but without the gaps created by class limits. they are obtained as follows: find the size of the gap between the upper class limit of one class and the lower classe limit of the next class, add half of that amount to each upper class limit to find the upper class boundaries and subtract half that amount from each lower class limit to find the lower class boundaries
class midpoints
midpoints of the classes, each class midpoint can be found by adding the lower class limit to the upper class limit and dividing the sum by two
class width
difference between two consecutive lower class limits or two consecutive lower class boundaries
bar graph in which horizontal scale represents calsses of data values and the vertical scale represents frequencies, the heights of the bars are drawn adjacent to each other (without gaps)
measure of center
a value at the center of middle of a data set
arithmetic mean
measure of the center found by adding the values and dividing the total by the number of values
measure of the center that is the middle value when the original data values are arranged in order of increasing (or decreasing) magnitude
value that occurs most frequently
two values occur iwth the same greatest frequency
more than two values occur with the same greatest frequency, each is a mode
measure of the center that is the value midway between the highest and lowest values inthe original data set, found by adding the highest data value to the lowerst data value and then dividing the sum by two
distribution of data is skewed if it is not symmetric and extends more to one side than the other
the difference in a set of data between the maximum and minimum value
standard of deviation
measure of the variation of values about the mean, it is a type of average deviation of values from the mean that is calculated
measure of variation equal to the square of the standard deviation
sample variance
square of the standard deviation s
population variance
square of the popluation standard deviation sigma
standardized score
z score-numer of standard deviations that a given value x is above or below the mean
5-number summary
consists of the minimum value, the first quartile (Q1), the median (or second quartile Q2), the third quartile (Q3), and the maximum value
box and whisker digram-graph of a data set that consists of a line extending from the minimum value to the maximum value, and a box with lines drawn at the first quartile, median and third quartile

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