# 3.17 Intro to Data Science: Measures of Central Tendency—Mean, Median and Mode¶

- Measures of central tendency:
  - mean—the average value in a set of values.
  - median—the middle value when all the values are arranged in sorted order.
  - mode—the most frequently occurring value.
- Each represents a “central” value in a set of values.
  - A value which is in some sense typical of the others.

In [1]:

    grades = [85, 93, 45, 89, 85]

In [2]:

    sum(grades) / len(grades)

Out[2]:

    79.4

- `sum` and `len` are both examples of functional-style programming reductions
- The Python Standard Library’s `statistics` module provides functions for calculating the reductions mean, median and mode.

In [3]:

    import statistics

In [4]:

    statistics.mean(grades)

Out[4]:

    79.4

In [5]:

    statistics.median(grades)

Out[5]:

    85

In [6]:

    statistics.mode(grades)

Out[6]:

    85

- Sorting `grades` helps you see the median and mode.

In [7]:

    sorted(grades)

Out[7]:

    [45, 85, 85, 89, 93]

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