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Data Analysis > Descriptive Statistics > Flashcards

Descriptive Statistics Flashcards

1
Q

Nominal data

A
  • No quantitative value
  • Categorised
  • No inherent order
  • Mode
    (e. g. Male or female, eye colour)
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2
Q

Ordinal

A
  • Ranked scale
  • Non-numeric concepts
  • Difference between values not know
  • Can’t define mean
  • Central tendency = median or mode
    (e. g. level of satisfaction - ‘very happy’, ‘happy’ etc.)
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3
Q

Interval

A
  • Known differences between values
  • No true zero
    (e. g. temperature)
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4
Q

Ratio

A
  • Order
  • Known differences between values
  • True zero
    (e. g. height/weight)
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5
Q

Converting between types of data

A
  • Divide numerical data into categories (e.g. small, medium, large)
  • Or use interval/ratio data to rank individuals
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6
Q

What are the three types of descriptive statistics?

A
  1. Central tendencies
  2. Dispersion
  3. Skewness and kurtosis
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7
Q

Why are descriptive statistics important?

A
  • First step in analysis
  • Provide an overview of characteristics of data
  • Summarise and describe a sample or population
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8
Q

Central tendencies

A
  • Grouping around the middle value

- Mean, median, mode

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9
Q

Dispersion

A
  • Measure of variation

- Range, interquartile range, standard deviation

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10
Q

Skewness and kurtosis

A

Describe the shape of distribution

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11
Q

Describe mean

A
  • Sum of values divided by number of observations
  • Interval or ratio
  • Good for large data set with expected normal distribution
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12
Q

What are the advantages/disadvantages of using mean?

A

+ All values are considered

- Distorted by extremes

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13
Q

Describe median

A
  • Values are ranked by magnitude
  • Median is the middle value (or half way between two middle values)
  • Ordinal, interval, ratio
  • Most useful when using symmetrical data
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14
Q

What are the advantages/disadvantages of using median?

A

+ Not influenced by extremes

- Widely differing data may have the same median

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15
Q

Describe mode

A
  • The most frequent value

- Nominal, ordinal

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16
Q

What are the advantages/disadvantages of using mode?

A

+ Useful to identify ‘typical figure’

- Not useful where no values reoccur (usually with interval/ratio)

17
Q

What are measures of dispersion?

A
  • Relate to the spread of values

- Compliment central tendencies in providing a more complete descriptive summary

18
Q

Describe range

A

Difference between the smallest and largest values

19
Q

What are the advantages/disadvantages of range?

A

+ Simple
+ Indicates degree of spread
- least informative - depends on extreme values

20
Q

Describe inter-quartile range

A
  • Difference between the highest quarter and lowest quarter of values when ranked
  • Measures spread about the median
21
Q

What do small/large interquartile ranges indicate?

A

Small - values are clustered around the median

Large - greater degree of spread

22
Q

What are the advantages/disadvantages of IQ range?

A

+ Not influenced by extremes - 50% of data used

+ Anomalies are not considered

23
Q

Describe standard deviation

A
  • Dispersion around the mean
  • Considers all values
  • Square root of variance
24
Q

What are the advantages/disadvantages of standard deviation?

A

+ Most reliable index of dispersion
+ Square root gives positive value - other mathematical uses
+ Adds up total deviation from mean across the whole set

25
Q

Describe variance

A
  • Coefficient of variation expresses variability of a percentage of the mean
  • Dispersion relative to size of observation
26
Q

What are the advantages/disadvantages of variance

A
  • Can be used to compare variables in different units of measurement
27
Q

Describe skewness

A
  • Indicator of distribution around the central value
  • Negative - skew to the right (mean < median)
  • Positive - skew to the left (mean> median)
28
Q

What is a normal curve?

A

A theoretical distribution representing a symmetrically distributed data set

29
Q

Describe kurtosis

A

The extent to which a frequency distribution is peaked or flat

30
Q

What are the three types of kurtosis

A
  1. Leptokurtic (+) – tall, narrow
  2. Platykurtic (-) – lower, wider
  3. Mesokurtic (0) – normal curve

Data Analysis (5 decks)

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