distributions

• mean


  add up all the numbers and divide by how many there are
• median


  place in order and the middle value
• mode


  most frequent value
• when do you use mode?

  if data is in categories (nominal)
• when do you use the median?

  if there's an outlier
• when do you use the mean?

  in all other situations
• why is the mean the best?

  it takes the size of every value into account
• distribution


  how the data is spread out
• positive skew


  -score bunched to left

  -most low scores

  -a few extreme high scores

  -mean is higher than the media & mode
• negative skew 


  -data is bunched to the right

  -mostly high scores with a few low

  -mean is lower than the media & mode
• when might we see a negative skew?


  when an exam is too easy
• normal distribution


  -mean, median & mode are all approximately equal

  -distribution is symmetrical around mid-point

  -dispersion of scores either side of mid-point is consistent
• how do we plot distributions?

  histogram
• label

  A) positive

  B) negative

  C) normal distribution