Notation

Data matrix

We will conventionally represent a data matrix by an upper-case and its component variables as or more commonly with a lower-case .

For example, the data matrix may represent the entirety of a data set on patients with inpatient hospital visits, with three variables: for a patient's age, for the number of days since their last inpatient hospital visit, and for the duration in days of their last inpatient hospital visit. As below,

And with data, we will conventionally use rows for each observation. Below is an example with a few rows of data,

Number of variables

This is the number of variables within the data set. If we are collecting data on the age, weight, and height of patients, then for that data set.

Number of observations

This is the sample size, or the observation size, for our data set.

Observation (row of data)

A particular row of data will appear as follow when ,

We look at the observation in a data set.

Variable (column of data)

A particular variable will appear as follows when ,

Data point

This refers to the observation for the variable. For example, if we have a data set of daily climate readings of maximum temperature, total precipitation, and maximum humidity, then and for we would examine total precipitation.