Statistics and parameters

To find out about a population we take a sample

Statistics describe features of the sample

What statistics do we use?

How are they calculated?

We use sample statistics to make inferences about population parameters

Proportion Central

tendency Variation or

spread Shape Unusual features

The Measures of Central TendencyThe Mean is easy to calculate and is also easily understood.

BUT! It is affected by extreme values.

The Measures of Central TendencyThe Median is unaffected by extreme values, but it is more difficult to calculate as the data has to be ordered first.

BUT! It is UNaffected by extreme values.

The Measures of Central TendencyThe Mode is useful to manufacturers who want to identify the most popular value.

BUT! It is not always typical of a population as a whole.

The Measures of Central TendencyThe Mean is easy to calculate and is understood.

BUT! It is affected by extreme values.

The Measures of SpreadThe Range is the difference between the maximum and minimum values. The range is easy to calculate and understand.

BUT! If there are extreme values, the range does not accurately reflect how spread out the data values are.

The Measures of SpreadThe Inter-quartile Range is the difference between the upper quartiles and the lower quartile and gives the range of the middle 50% of the data.

As the extreme values are outside the middle 50% of the data, the inter-quartile range gives a clear indication of the spread.

The Measures of SpreadThe Standard deviation is a calculated measure of spread which is shows how much variance there is from the mean.

You can safely conclude that a set of data with a larger standard deviation is more spread out than a set of data with a smaller standard deviation.