Biostat Mod 4: Data Organization in Biostatistics and Epidemiology

Raw Data

Set of data in its original form. Example: Final Grades of MLS Students in Biostatistics.

Array

Arrangements of observations according to their magnitude, either increasing or decreasing. Importance: Easier to detect the smallest and largest value, easier to find the measures of position. Example: Final grades of MLS Students in Biostatistics.

importance of array

easier to detect smallest and largest value, easier to find the measures of position

Class Frequency

Number of observations falling in the class.

Class Interval

Numbers defining a class.

Class Limits

End numbers of the class.

Class Boundaries

upper class and lower class boundaries

Lower class boundaries (LCB)

halfway between the lower-class limit of the class and the upper-class limit of the preceding class.

Upper class boundaries (UCB)

halfway between the upper-class limit of the class and the lower-class limit of the next class.

Class Size

Computed by using the respective class limits instead of class boundaries.

Open-end Class

A class that has no lower-limit or upper-limit.

Sturge's Formula

Can be used as a first approximation to compute the number of classes.

equation for sturge's formula

K = 1 + 3.322 log n

Relative Frequency Distribution

Number of times a value of the data occurs in the set of all outcomes to the total number of outcomes.

Relative Frequency Percentage

Number of times a value of the data occurs in the set of all outcomes to the total number of outcomes times 100.

Cumulative Frequency Distribution

Shows the accumulated frequencies of successive classes, beginning at either end of the distribution.

Greater than CFD (>CFD)

shows the number of observations greater than the Lower-Class boundary (LCB).

Less than CFD (<CFD)

shows the number of observations less than the Upper-Class boundary (UCB).

Frequency Distribution Histogram

A bar graph that displays the classes on the horizontal axis and the frequencies of the classes on the vertical axis ; the vertical lines of the bars are erected at the class boundaries and the height of the bars corresponding to the to the class frequency

difference of bar graph and histogram

With bar charts, each column represents a group defined by a categorical variable; with histograms, each column represents a group defined by a continuous, quantitative variable.

Frequency Polygon

A line chart constructed by plotting the frequencies at the class marks and connecting the plotted points by means of straight lines ; polygon is closed by considering an additional class at each end and the ends of the lines are brought down to the horizontal axis at the midpoints of the additional classes.

Stem-and-Leaf Plot

Alternative method for describing a set of data. Presents a histogram-like picture of the data while retaining the actual observed values of each data point. Partly tabular and partly graphical in nature.