Maths for Clinicians 3

• What is a variable?

  A quantity that varies
• Compare research study data to routinely collected data:

  • Better quality
  • More expensive
  • More time consuming
• What are the categorical variables?

  • Ordinal (e.g, ranking of pain- low, moderate & severe)
  • Nominal (e.g, ethnic group (unordered))
  • Binary (e.g, yes or no)
• What can categorical variables be created from?

  Numerical variables
• What are the numerical variables?

  • Continuous (e.g, height)
  • Discrete (e.g, number of siblings)
• How can 1 categorical variable be presented?

  • Bar chart
  • Pie chart
  • Frequency table
• How can 1 continuous variable be presented?

  • Histogram
  • Bar chart
• How can 1 discrete variable be presented?

  Bar chart
• When do you use a contingency table to display data?

  • Categorical outcome
  • Categorical exposure
• When do you use a box and whisker plot to display data?

  • Numerical outcome
  • Categorical exposure
• When do you use a scatter plot to display data?

  • Numerical outcome
  • Numerical exposure
• Which variables can be used to describe height?

  • Continuous
  • Ordinal
  • Binary
• What is exposure & outcome?

  Exposure = Independent variable/risk factor

  Outcome= Dependent variable/response variable
• Normal distribution uses...

  • Mean (location of distribution)
  • Standard deviation (variability) (spread of observations around the mean)
• Not normal distribution uses...

  • Median (location of distribution)
  • Interquartile range (variability)
• What is a negatively skewed distribution?

  Tail is longer on the left side

  (left foot)
• What is a positively skewed distribution?

  Tail is longer on right side

  (right foot)
• How do you calculate variance?

  Standard deviation squared
• How do you calculate the median?

  • Middle value
  • n + 1 / 2
• What is the mode?

  • Most common data set
  • Shouldn't exist if data truly continuous
• What is a disadvantage of the range?

  Relies on extreme values
• What is a reference range?

  95% reference range = mean +- 1.96 x SD

  (likely values for an individual in a population)
• What is the equation used to calculate standard deviation?

  Sum of (each value - mean)2 / number of observations - 1