Measures of Central Tendency

Measures of central tendency provide information about a “typical” observation in the data. Such measures are usually computed from sample data, rather than from population data.
STATISTIC AND PARAMETER
A statistic is a descriptive measure computed from a sample of data. A  parameter is a descriptive measure computed from an entire population of data.

The Mean and the Median

The most common measures of central tendency is the arithmetic mean, usually referred to simply as the “mean” or the “average”.

ARITHMETIC MEAN

The arithmetic mean of a set of data is the sum of the data values divided by the number of observations. If the data set is from a sample, then the sample mean,
                 

n = sample size.
Example: People across the country participate in various walks to raise funds for needed research. Recently, national and local business sponsored a Suntan G. Komen Breast Cancer Foundation 5K “Race for the Cure” in Daytona Beach, Florida. Participants could either run or walk the race. The time to complete the race appeared on a large display as each participant enthusiastically crossed the finish line. The times (rounded to the nearest minite) for a random sample of 5 participants who walked this race are:
                         45    53    45   50   48
Compute the mean times for this random sample of participants.
Solution:
The sample mean time is easily found to be