Summary: Statistics I

Read the summary and the most important questions on Statistics I

• Levels of measurement

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• What is a variable?

  Anything that can be measured and can differ across entities or across time (e.g hair color, level trust in government, age)

• What is the difference between the independent and dependant variables?

  Independent (X) = proposed cause (predictor variable)
  Dependant (Y) = proposed effect (outcome variable)
  The Independent variable has an effect on the dependant variable. 

• What are the categorical levels of measurement?

  Nominal: 
  - two+ exclusive categories (hair color)
  - no natural order
  - No arithmetic operations possible (subtraction, equal to) but the frequency (mode) (e.g occupation, political party affiliation)
  
  Ordinal: 
  - There is a clear ordering of the values (e.g low-high, little-much, small-large -> think of how much you agree with a statement)
  - spacing between values, not the same across the levels (can't say to full agree is 5 times as much as not agree)
  - Comparison possible but only relative ( level of agreement, level of education, political interest)

• Measures of dispersion

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• What are the different measures of dispersion?

  Nominal- no measure of dispersion possible (no natural order)
  Ordinal - range, inter-quartile range
  Interval-ratio - Range, inter-quartile range, variance/standard deviation 

• What if you have an even set of numbers?

  Split it in the middle and take the middle number of each half

• Introduction

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• What are the golden rules for statistics?

  1. Read and re-read the chapters 
  2. Watch the web-lectures and attend the Q&A lectures
  3. Attend and participate in all seminars
  4. Make the assignments and practise with the materials

• Distributions and measures of central tendency

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• How can we describe different distributions?

  The measure of central tendency - a value that that attempts to describe a set of data by identifying the central position within that set of data
  Measure of dispersion - how stretched or squeezed is the distribution

• What are the levels of measures of central tendancy?

  Nominal - mode
  ordinal - median+mode
  Interval & ratio - mean+median+mode

• Standard normal distribution + z scores

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• What is a symmetrical distribution?

  Evenly concentrated, mean, median and mode are at the top of the mountain.

• What is a bimodal distribution?

  It means that it has two modes (two waves)