Part 6: Statistics

• A population is all the people, events or items which are of interest to be questioned, surveyed, or experimented on.
• A census collects information from all members of a population.
• Questionnaires are used to collect responses from people in a population by asking questions
• Sampling involves selecting a smaller sub-group of people or objects from a population to test a theory or idea (a hypothesis) about the population
• Two-way tables can be used to display information from a survey or experiment with two variables.

  
• Bar charts are for displaying discrete qualitative data.

  
• Pictograms make data easy to visualise, although they aren’t always as accurate as other charts. They use symbols to represent a set frequency of an item, and include a key to show how much of each quantity each symbol represents

  
• Vertical line graphs are for discrete quantitative data

  
• Discrete data – data that must take one of a set of certain values
• Grouped discrete data – data points are given as values within a group.
• Continuous data – numerical data which can take any value in a given range. Examples include age, height and weight
• We use histograms to display continuous grouped data.

  
• Cumulative frequency graphs show the total frequencies of grouped data at fixed points

  
• Primary data is collected by the person carrying out the research. It could be collected by the researcher in a survey or questionnaire.
• Secondary data is data collected by somebody else.
• Box plots show the median and quartiles of a set of data

  
• Range = Maximum Value - Minimum Value
• Interquartile Range (IQR) = Q3 - Q1

  
• The mode is the most common value or values.
• The median is the middle value when the data is in numerical order
• The mean of a set of data is the sum of all the values divided by the number of values

  Mean = $\frac{Sum\ of\ values}{Total\ number\ of\ values}$
• In a scatter graph, the closer the points are to representing a straight line, the more correlated they are said to be.
• In a scatter graph, the closer the points are to representing a straight line, the more correlated they are said to be

  
• Positive correlation = As the variable on the x-axis increases, the variable on the y-axis increases. The line of best fit has a positive gradient.

  
• No correlation = There is no relationship between the two sets of data. There is no identifiable line of best fit.

  
• Negative correlation = As the variable on the x-axis increases, the variable on the y-axis decreases. The line of best fit has a negative gradient.