M2 - Tutorial Descriptive Statistics Flashcards

1
Q

Arithmetic mean

A

durschschnitt aller werte

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2
Q

Median

  • uneven n
  • even n
A
  • for uneven n the xmed is the value sin the middle of a sorted list
  • for even n the xmed is the arithmetic mean of the two values in the middle
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3
Q

Mode

A

most frequent parameter value

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4
Q

p-quantil

e.g.

A

values which divide the n values into two parts, of which at least a fraction p of the data is less/equal to xp, and at least a fraction 1-p is greater/equal xp

10% quantil: mind 10% der daten sind kleiner/gleich x10% und 90% der daten sind größer/gleich x10%

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5
Q

variance s²

A

measures the spread of data around the mean

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6
Q

standard deviation

  • if small
  • if large
  • advantage over variance
A

used to quantify the amount of variation of a set of data values

  • if small, the data points are close to the mean
  • if high, the data points are spread out over a wider range
  • it is expressed in the same unit as the data (unlike variance)
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7
Q

advantage coefficient of variance

A

it is irrespective of scale –> appropriate for comparing different spreads

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8
Q

skewness & coeff. of skewness

  • left
  • right
  • symmetric
A
  • left-skewed: the bigger part of the distribution is concentrated on the right gm < 0
  • right-skewed: the bigger part of the distribution is concentrated on the left gm > 0
  • symmetric: right and left half are almost mirror-image
    gm = 0
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9
Q

Kurtosis / Peakedness

  • peaked
  • flattened
  • normal
A
  • how sharp?
  • peaked: leptokurtic distribution y > 0
  • flattened: platykurtic y < 0
  • normal: mesokurtic y = 0
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10
Q

Digression: Data types

A
  • nominal: a few possible values
  • ordinal: few ranked values
  • interval: any value within a certain interval; no meaningful zero
  • ratio: numbers, with meaningful zero denoting that there is no variable
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11
Q

creation of dummy variables

  • why
  • how
A
  • why? if there is a binary variable (=1/0; yes/no), which is indicator for a continuous variable
  • create dummy for every state (=1, set all others = 0)
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