Levels of data, measures of central tendancy, dispersion. and distribution are noted.

What are levels of data and central tendancy? How is the standard deviation and semi-interquartile range calculated?

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...freak samples:

e.g. 1,2,3,(4),5,5,79 - the middle value (median) = 4

The median value can however be distorted by small samples.

MEAN - This is the average value of the scores. This the most suitable measure for interval and ration level data. This method can, however be distorted by extreme 'freak' values.

e.g. 3,5,4,4,6,6,7 - the mean = 5

Measures of dispersion

Measures of dispersion are used to estimate the spread of values from the average. Values may be close to the average or widely spread from the average.

RANGE - The range is the different between the smallest and the largest values. This is quick and very easy to calculate. It is at a disadvantage as it can be distorted by extreme freak values.

SEMI-INTERQUARTILE RANGE - This method can be used with ordinal or interval level data that is not normally distributed. First that data is placed in order and the lower quartile (Q1) ...