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Descriptive Statistics

Mean, Median and Mode

Mean, Median and Mode are all measures of central tendency.

• Mean, a.k.a. average, is sum of values divided by count of values.
• Median – if we order from smallest to largest, this will be the middle value. For an even number of values, we have two middle values and we split the difference.
• Mode – the most popular value

Question: What are the mean, median and mode of the data below?

Answer: What are the mean, median and mode of the data below?

Standard Deviation

The standard deviation (SD) is a measure of how spread out the numbers are.

In a normal (bell shaped) curve

• 68% within 1 SD of the mean
• 95% within 2 SD of the mean

The Standard Deviation formula

A cautionary tale – Anscombe’s Quartet

Source: Wikipedia

Exercise: London Bike Hire Dataset

Transport for London (TfL) introduced bike hire in 2010. This dataset has the number of bikes hired every day from 30th July 2010 to this year.

The original data comes comes from the London Datastore, a free open public data portal run by the GLA and the Mayor of London. yiu can access it here.

Download the dataset here.

The first few rows of the data look like this.

Tasks

Analyse the data with Excel, Power BI or any tool that you prefer. The following questions below serve to start your analysis but feel free to ask other questions.

• How many observations? What are the start & end dates? Is this a continuous dataset with vaues for every date between the start and end date or are there any gaps?
• Get some descriptive stats on this dataset: e.g., min, max, median, mean, standard deviation
• Visualise the data:
  • the entire series as bar / line chart
  • by day of week and by year as a box-whisker chart (or matrix)
  • as a histogram
• What does each chart tell us about the data?