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You must be hungry 😋 > Statistics > Flashcards

Statistics Flashcards

1
Q

Population

A

The whole set of items that are of interest

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2
Q

Sample

A

A subset of the population intended to represent the population

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3
Q

Sampling unit

A

Each individual item in the population that can be sampled

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4
Q

Sampling frame

A

Sampling units of a population are individually named or numbered to for a list e.g. DVLA list of drivers and car registration, patients at a doctors surgery

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5
Q

Census

A

Data collected from the entire population

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6
Q

Census advantages

A

Should give completely accurate results

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7
Q

Census disadvantages

A
  • Time consuming & expensive

- Can not be used with tests involving destruction

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8
Q

Sampling advantages

A
  • Cheaper, quicker

- Less data to process

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9
Q

Sampling disadvantages

A
  • Data may not be accurate

- Data may not be large enough to represent small sub-groups

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10
Q

How do you carry out simple random sampling?

A

In a sampling frame, each item is assigned a number. Use a random number generator to select a random item or ‘lottery sampling’

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11
Q

Simple random sampling advantages

A
  • Bias free
  • Easy + cheap
  • Each number has a known equal chance of being selected
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12
Q

Simple random sampling disadvantages

A
  • Unsuitable for large population sizes
  • Sampling frame needed
  • Can introduce bias if the sampling frame is not random
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13
Q

How do you carry out systematic sampling?

A
  • > Required elements are chosen at regular intervals in an ordered list
  • Take every Kth element where: K= population size(N)/sample size(n)
  • Starting at a random item between 1 and K
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14
Q

Systematic sampling advantages

A
  • Simple and easy to use

- Suitable for large samples

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15
Q

Systematic sampling disadvantages

A
  • Sampling frame needed

- Can introduce bias if sampling frame is not random

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16
Q

How do you carry out stratified sampling?

A

Divide population into strata (groups) and a simple random sample is carried out in each group
- Sample size(n)/population size(N) sampled from each strata

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17
Q

Stratified sampling advantages

A
  • Reflects population structure

- Guarantees proportional representation of groups within population

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18
Q

Stratified sampling disadvantages

A
  • Population must be clearly classified into distinct strata

- Selection within each stratum suffers from same disadvantages as simple random sampling

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19
Q

How do you carry out quota sampling?

A
  • Population is divided into groups according to characteristics
  • A quota of items in each group is set to reflect the proportion in the whole population
  • Interviewer selects the actual sampling unit
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20
Q

Quota sampling advantages

A
  • Allows small sample to still be representative of population
  • No sampling frame required
  • Relatively easy & inexpensive
  • Allows for easy comparison between different groups of a population
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21
Q

Quota sampling disadvantages

A
  • Non-random sampling can introduce bias
  • Population must be divided into groups which can be costly or inaccurate
  • Increasing scope (further investigation) of the study increases number of groups adding time and expense
  • Non-responses are not recorded
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22
Q

How to carry out opportunity sampling?

A

Sampling taken from people who are available at the time of study who meet criteria

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23
Q

Opportunity sampling advantages

A
  • Easy to carry out and inexpensive
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24
Q

Opportunity sampling disadvantages

A
  • Unlikely to provide a representative sample

- Highly dependant on individual researcher

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25
Q

Quantitative values

A

Variables or data associated with numerical values e.g. shoe size

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26
Q

Qualitative values

A

Variables or data associated with non-numerical values e.g. hair colour

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27
Q

Continuous variable

A

A variable that can take any value within a given range e.g. time: 1 second, 1.1 seconds, 1.01 seconds

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28
Q

Discrete variable

A

A variable that can only take a specific value in a given range e.g. number of kids; you cannot have 4.69 children

29
Q

What values do daily total sunshine, daily mean wind speed and daily max gust take for the first two weeks of May 1987 in the UK

A

n/a

30
Q

Value for trace

A

0.025

31
Q

Leuchars (UK)

A
  • Sheltered by the Ochil hills on the west and exposed to the North Sea on the east
  • Most northern UK weather station so it has the lowest average temperatures
32
Q

Leeming (UK)

A
  • Situated between Yorkshire dales to the west and north York Moore to the east
  • Sheltered location leads to a dry, almost semi-arid climate
33
Q

Heathrow airport (UK)

A
  • Far from the city centre so the temperature aren’t raised by the urban heat island effect
  • Below-average rainfall for Britain
  • Hotter summer temperatures due to its proximity to continental
    Europe and its southerly latitude
34
Q

Hurn (UK)

A
  • 6km from the south coast of England

- Has rainfall well below the national average

35
Q

Camborne (UK)

A
  • Mildest and sunniest climate in UK
  • In some places it is sub tropical because of its southern location and also the warm water of the Gulf Stream
  • Presence of sea moderates extreme temperatures
  • Extreme rainfall is not uncommon
36
Q

Beijing (INT)

A
  • Shielded by mountains to the north and west
  • It has a humid continental climate
  • East Asian monsoon causes humid summers
  • Siberian anticyclone causes cold, windy and dry winters
37
Q

Jacksonville (INT)

A
  • Humid subtropical climate
  • Winters are typically mild and sunny as it is low lying on the coast
  • Summers are usually hot, very humid and prone to thunderstorms
  • High humidity makes high heat common in the summer
38
Q

Perth (INT)

A
  • Hot summer Mediterranean climate
  • Winters are generally cool and wet
  • Summer months are hot, dry and sunny
  • Summer rainfall usually caused by short thunderstorms or decaying tropical cyclones
39
Q

Daily mean temperature (°c)

A

Average of the hourly temperature readings during a 24 hr period

40
Q

Daily total rainfall

A

Includes solid precipitation such as snow and hail which is melted befor being included in any measurements

41
Q

Daily total sunshine

A

Recorded to the nearest tenth of an hour

42
Q

Daily mean wind direction and wind speed

A
  • Measured in knots
  • Averaged over 24 hours
  • Mean wind directions are given as bearing and as cardinal (compass) directions
  • Data for mean wind speed categorised according to the Beaufort scale
43
Q

Daily maximum gust

A
  • Measured in knots
  • Highest instantaneous wind speed recorded
  • Direction is also recorded
44
Q

Daily maximum relative humidity

A
  • Percentage of air saturation with water vapour

- Humidities above 95% gives rise to duty and foggy conditions

45
Q

Daily mean cloud cover

A
  • Measured in oktas

- Eighths of the sky covered in clouds

46
Q

Daily mean visibility

A
  • Measured in decametre

- Greatest horizontal distance at which an object can be seen in daylight

47
Q

Daily mean pressure

A

Measured in hectapascals

48
Q

Measures of location

A

Single values which describe a position in a data set

49
Q

Variance

A

The average squared distance of each value from the mean

50
Q

Standard deviation

A

(Variance)^1/2

51
Q

Outlier

A

An extreme value that goes outside the overall pattern of the data

52
Q

Cleaning the data

A

Process of removing anomalous from a data set

53
Q

What do you compare between two sets of data

A

Measure of location and measure of spread

54
Q

Equation for frequency density

A

Frequency / class width

55
Q

What is an experiment

A

A repeatable process that gives rise to a number of outcomes

56
Q

What is an event?

A

A set of one or more of these outcomes (we often use capital lettered to represent this)

57
Q

What is a sample space?

A

Set of all the possible outcomes

58
Q

Mutually exclusive events

A

Two things that cannot happen at the same time hence why they do not share an intersection in a Venn diagram

59
Q

The event A and B

A

The intersection of both A and B, it represents the event that both A and B occur

60
Q

The event A or B

A

Also known as the union of A and B, it represents the event of A or B, or both, occur

61
Q

The event not A

A

Also known as the complement of A representing the event that A does not occur

62
Q

You can model a random variable with binomial distribution if:

A
  • There are a fixed number of trials
  • There are two possible outcomes: ‘success’ or ‘failure’
  • There is a fixed probability of success
  • The trials are independent of each other
63
Q

Test statistic

A

Evidence from the sample in a hypothesis test

64
Q

Null hypothesis

A

Is the current position that nothing has changed unless proven otherwise
-> In binomial hypothesis testing it will always be that the probability equals a specific value

65
Q

Alternative hypothesis

A

There is some change in the population parameter

66
Q

When do you use a one tailed test?

A

If the alternative hypothesis is H1:p>a (probability greater than expected) or H1:p<a></a>

67
Q

When do you use a two tailed test?

A

If the alternative hypothesis is H1: p does not equal a (probability is different than expected)

68
Q

Critical region

A

The values for which you would reject the null hypothesis

69
Q

Critical value

A

The first value to fall inside the critical region

You must be hungry 😋 (6 decks)

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