Mean
The Mean is the average of the scores.  It is calculated by adding up the scores and dividing this value by the number of scores.

Median
The Median is the midpoint of a series of numbers.  The median is found by arranging values in order and then selecting the one in the middle.  In the case of an even number of values, the median is calculated by taking the average of the two numbers in the middle.   For example, to calculate the median of this group of numbers: 1, 4, 5, 7, 12, 20; take the average of 5 and 7, which is 6.

Medians can be especially useful when working with a statistically skewed series of values.  For example, medians are often used to describe family income.  If you had a group of 5 persons with annual incomes of 3 million, $35,000, $30,000, $25,000, and $20,000, the mean would be $622,000 and the median would be $30,000.  The median would provide a better sense of where the group was as a whole than the mean.  The mean value can be heavily impacted by a small proportion of the values.

Membership
These are persons who have formally joined a church.  They are persons who have been baptized and have publicly declared their faith.  Typically, this does not include any young children.  The practice in many United Methodist churches is for those who are in sixth grade to participate in confirmation and to make a decision about if they are ready to profess their faith and join the church.   The term Professing Members is often used.

Average Annual Worship Attendance
This value is determined by taking the mean of the number of persons at the principal weekly worship services for a year.  For most churches this refers to their Sunday morning services.  However, some churches include services that occur on Saturday evening or Sunday afternoon.  When comparing years, keep in mind that extraneous factors can create variability. These include weather (icy roads, rain, . . .) and calendar issues like January 1 falling on a Sunday. (Worship Attendance statistics for a specific year are only attributed to a pastor when that person served the church for the full year.)

Profession of Faith
This is the number of persons who joined the church who are not transferring from another church.   This includes youth who complete confirmation and decide to join the church.  It also includes youth and adults who simply step forward and express that they want to join the church who have never done this before.

PF-WA Index:  This index denotes how many persons jointed by profession of faith for every 100 persons in worship each week.  (The profession of faith value is divided by average annual worship attendance and multiplied by 100.) 

WA-MEM Index:  This index denotes ratio between average annual worship attendance and the number of church members (professing members).  (The average annual worship attendance value is divided by church membership and reported as a percentage. ex. 100 worship attendance / 300 members = 33.3%)