BIOSTATISTICS and EPIDEMIOLOGY: Lesson 2, 3 and 4 TERMINOLOGIES

Frequency Distribution

a table that shows classes or intervals of data with a count of the number in each class.

class width

the distance between lower (or upper) limits of consecutive classes.

range

is the difference between the maximum and minimum data entries.

midpoint

is the sum of the lower and upper limits of the class divided by two. The ___ is sometimes called the class mark

relative frequency

the portion or percentage of the data that falls in that class.

cumulative frequency

the sum of the frequency for that class and all the previous classes.

frequency histogram

is a bar graph that represents the frequency distribution of a data set.

Class boundaries

are the numbers that separate the classes without forming gaps between them.

frequency polygon

is a line graph that emphasizes the continuous change in frequencies.

relative frequency histogram

has the same shape and the same horizontal scale as the corresponding frequency histogram.

cumulative frequency graph

also known as ogive, a line graph that displays the cumulative frequency of each class at its upper class boundary.

stem-and-leaf plot

each number is separated into a stem (usually the entry’s leftmost digits) and a leaf (usually the rightmost digit). This is an example of exploratory data analysis.

dot plot

each data entry is plotted, using a point, above a horizontal axis.

pie chart

a circle that is divided into sectors that represent categories. The area of each sector is proportional to the frequency of each category.

Pareto chart

a vertical bar graph is which the height of each bar represents the frequency. The bars are placed in order of decreasing height, with the tallest bar to the left.

paired data sets.

When each entry in one data set corresponds to an entry in another data set, the sets are called __.

time series

A data set that is composed of quantitative data entries taken at regular intervals over a period of time.

time series chart

is used to graph a time series.

mean

the sum of the data entries divided by the number of entries.

median

the value that lies in the middle of the data when the data set is ordered.

mode

is the data entry that occurs with the greatest frequency.

outlier

a data entry that is far removed from the other entries in the data set.

symmetric

A frequency distribution is ___ when a vertical line can be drawn through the middle of a graph of the distribution and the resulting halves are approximately the mirror images.

uniform

A frequency distribution is ___ (or rectangular) when all entries, or classes, in the distribution have equal frequencies. A ___ distribution is also symmetric.

skewed

A frequency distribution is ___ if the “tail” of the graph elongates more to one side than to the other.

skewed left

A distribution is ___ (negatively skewed) if its tail extends to the left.

skewed right

A distribution is ___ (positively skewed) if its tail extends to the right.

coefficient of variation

the standard deviation divided by the mean. The result is expressed as a percentage.

Pk percentile

defined to be that numerical value such that at most k% of the values are smaller than Pk and at most (100 – k)% are larger than Pk in an ordered data set.

Deciles

divide the data set into 10 groups.

Quartiles

divide the data set into 4 groups.

Probability Experiment

- is a chance process that leads to well defined results called outcomes.

Outcomes

is the result of a single trial of a probability experiment.

Sample Space

is the set of all possible outcomes of a probability experiment.

event

consists of a set of outcomes of a probability experiment.

Classical Probability

If an event can occur in N mutually exclusive and equally likely ways, and if m of these possess a trait E, the probability of the occurrence of E is equal to m/N.

Relative Frequency Probability

If some process is repeated a large number of times, n, and if some resulting event with the characteristic E occurs m times, the relative frequency of occurrence of E, m/n, will be approximately equal to the probability of E.

sensitivity

probability of a positive test result given the presence of a disease.

specificity

probability of a negative test result given the absence of a disease.

predictive value positive

the probability that a subject has the disease given that the subject has a positive screening test result.

predictive value negative

the probability that a subject does not have the disease given that the subject has a negative screening test result.