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AP0609 - Advanced Analytical Techniques > Measurements and Descriptive Stats > Flashcards

Measurements and Descriptive Stats Flashcards

1
Q

Define ‘population’

A
  • every member with selected characteristic
  • e.g. humans born in UK
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2
Q

Define ‘sample’

A
  • subset of given sample which represents the population
  • unrelated
  • chosen at random
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3
Q

Define ‘variable’

A
  • any characteristic or property that can take one of a range of values
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4
Q

Define ‘parameter’

A
  • numerical constant in any particular instance
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5
Q

Define ‘data’

A
  • refers to items of information
  • singular = datum, or data value
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6
Q

Name the 3 types of data

A
  • quantitative
  • ranked
  • qualitative
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7
Q

Define ‘quantitative data’

A
  • characteristics whose differing states can be described by ‘real’ numbers
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8
Q

Define ‘ranked data’

A
  • ordinal scale, ranked in order of magnitude
  • e.g. order of birth of children in a family
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9
Q

Define ‘qualitative data’

A
  • categorical; not measured against numerical scale nor ranked
  • non numerical and descriptive
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10
Q

Name the 3 types of quantitative data

A
  • continuous
  • discontinuous
  • derived data
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11
Q

Define ‘continuous data’

A
  • obtained by measurement
  • usually measured against numerical scale
  • significant figures/decimal places
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12
Q

Define ‘discontinuous data’

A
  • obtained by counting
  • data must be whole numbers
  • e.g. number of colonies on Petri dish
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13
Q

Define ‘derived data’

A
  • calculated from direct measurements
  • e.g. ratios, percentages, rates etc.
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14
Q

Name 4 types of measurement scales

A
  • nominal
  • ordinal
  • interval
  • ratio
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15
Q

What is a nominal scale?

A
  • classifies objects into categories based on descriptive characteristic
  • only scale suitable for qualitative data
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16
Q

What statistics are used with a nominal scale?

A
  • only those based on frequency of counts made: contingency tables, frequency distributions etc.
  • Chi-squared test
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17
Q

What is an ordinal scale?

A
  • classifies by rank
  • used with ranked data
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18
Q

What statistics are used with ordinal scales?

A
  • non-parametric methods, sign tests
  • Mann-Whitney U-test
19
Q

What is an interval scale?

A
  • numbers on equal-unit scale are related to arbitrary zero point
  • used for quantitative data
20
Q

What statistics are used with interval scales?

A
  • almost all types of test; t-test, analysis of variance (ANOVA) etc.
21
Q

What is a ratio scale?

A
  • similar to interval scale, except that the zero point now represents an absence of that character (i.e. it is an absolute zero)
22
Q

What statistics are used with ratio scales?

A
  • almost all types of test; t-test, ANOVA etc.
23
Q

Define ‘accuracy’

A
  • closeness of measurements to true value
24
Q

Define ‘precision’

A
  • closeness of repeated measurements to each other
25
Q

Define ‘bias’

A
  • consistent non-random divergence from accuracy
  • can be subjective, personal, or from incorrectly calibrated instruments
26
Q

Define ‘mean’

A
  • average value of data
  • obtained from sum of all data values divided by number of observations
27
Q

Advantages and disadvantages of the mean

A

Advantages
- good measure of centre of symmetrical frequency distributions
- uses all of the numerical values of sample, therefore incorporates all information content of data
Disadvantages
- value of mean is greatly affected by presence of outliers (values much smaller or bigger than most data)

28
Q

Define ‘median’

A
  • mid-point of observations when ranked in increasing order
  • represents location of main body of data better than mean when distribution is asymmetric or when there’s outliers in sample
29
Q

Define ‘mode’

A
  • most common value in sample
  • provides rapidly and easily found estimate of sample location, unaffected by outliers
  • however is affected by chance variation in shape of samples distribution, may lie distant from obvious centre of distribution
30
Q

Define ‘range’

A
  • difference between largest and smallest data values in sample
31
Q

Advantages and disadvantages of range

A

Advantages
- easy to determine
Disadvantages
- greatly affected by outliers, makes it a poor measure of dispersion

32
Q

Steps in calculating a semi-interquartile range for a data set

A
  • rank observations in ascending order
  • find values of 1st and 3rd quartiles
  • subtract value of 1st quartile from 3rd quartile
  • halve this number
33
Q

Advantages and disadvantages of semi-interquartile range

A

Advantages
- appropriate measure of dispersion with the median being the appropriate stat to describe location
Disadvantages
- can only be estimated for data grouped in classes
- takes no account of distribution shape at its edges
-

34
Q

What is the ‘five-number summary’?

A
  • consists of 3 quartiles and 2 extreme values; commonly presented as box-and-whisker plot
  • upper extreme, upper quartile, median, lower quartile, lower extreme
35
Q

Define ‘sample variance’

A
  • sum of squared deviations of each data value from the mean divided by n - 1 (where n is sample size)
36
Q

Define ‘standard deviation’

A
  • positive square root of sample variance
  • SD=√ (Σ(X – mean) 2) ÷ (n - 1)
37
Q

Define ‘coefficient of variance’ (CV or CoV)

A

-dimensionless measure of dispersion
- expresses SD as a percentage of sample mean
- (SD ÷ mean) x 100
- e.g. mean = 5; SD = 2; CoV = (2÷5) x 100 = 40%

38
Q

Define ‘unimodal distribution’

A
  • one peak
  • may be symmetrical or asymmetrical
39
Q

Define ‘bimodal distribution’

A
  • two peaks (two unimodal distributions
  • 2 populations are being sampled
40
Q

Define ‘polymodal distribution’

A
  • more than two peaks/unimodal distributions
  • more than two populations being sampled
41
Q

Define ‘positive skewness’

A
  • longer tail of distribution occurs for higher values of measured variable
42
Q

Define ‘negative skewness’

A
  • longer tail occurs for lower values
43
Q

Define ‘kurtosis’

A
  • name given to pointedness of frequency distribution
44
Q

Name the 2 types of kurtosis and what they mean

A
  • platykurtic; flattened peak
  • leptokurtic; pointed peak

AP0609 - Advanced Analytical Techniques (10 decks)

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