Sectieoverzicht

  • To make sense of data we need to condense it or organise it in a way that makes interpretation easier. The method used to condense or summarise the data depends on whether data are grouped or un-grouped. Remember that ungrouped data is unorganised or raw data. And, grouped data has been organised in some way.

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      Frequency distribution

      Before you summarise data, it is important to understand how to organise data using frequency distributions. By counting how often data values appear we can make a frequency distribution. The next video gives an example of how to organise data using a frequency distribution also called a frequency table. 

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      Cumulative frequencies

      Some graphs that represent data from a grouped frequency distribution need cumulative frequencies. Cumulative means to add up or collect values together.

      You can think of cumulative frequency as the running total of frequencies in a frequency distribution. This means you are adding a value to all of the values that came before it.

      To find the cumulative frequencies, add all the previous frequencies to the frequency for the current row, as shown in the table. Cumulative frequency table of ages


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      Measures of central tendency

      We gain a better understanding of data by summarising it numerically using statistics. Two types of summary measures that are used are; measures of central tendency (averages) and measures of dispersion (spread).

      You can read more about summarising data in: Revise measures of central tendency.

      You can watch the next video for an introduction to averages. 

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      Calculate averages

      Try the next exercise to see if you understand how to calculate the mean, median and mode. 

      Mean, median and mode practise. 

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      Measures of dispersion

      The measures of central tendency do not fully describe a data set and can often be misleading if we do not know how spread out or variable the data are. To work out the variation in data we have to calculate measures of dispersion.

      You can discover more about variation in data by going through the exercises in: Measures of dispersion. 

      The following video takes a closer look at how to calculate the interquartile range.

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      Calculate measures of dispersion

      The next 2 exercises will test your ability to calculate the range and interquartile range.

      Interquartile range

      Comparing the range and IQR