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Stats Flashcards

(40 cards)

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1
Q

What is population

A

The complete set of items you are interested in

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2
Q

What is a census

A

The measurement of values from every member of the population

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3
Q

What is a sample

A

A selection os observations taken from a subset of the population which is used to try to find out information about the population as a whole

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4
Q

what is the advantage of a census

A

You get a completely accurate view of the population

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5
Q

What is the disadvantage of a census

A
  • time consuming and expensive
  • cannot be used when the testing process destroys the items
  • not possible if the population is continually changing
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6
Q

What is the advantage of samples

A
  • less time consuming and expensive than a census
  • fewer people have to respond - so preferable when the population is large
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7
Q

What is the disadvantage of samples

A
  • the data may not be representative of the original population
  • the sample may not be large enough to give information about small minority sub-groups of the population
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8
Q

Why does the size of the sample matter, why

A

It can affect the validity of any conclusions drawn
Larger samples are more accurate (but need more resources)

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9
Q

What do different samples lead to

A

Can lead to different conclusions dues to the natural variation in a population

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10
Q

What are sampling units

A
  • Individual items of a population
  • E.g. 11 set 1 might form a population of mathematicians
  • Each student would be a sampling unit
  • Year 11 would be the population
  • Each student within each math set would be a sampling element
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11
Q
A
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12
Q

What is a sampling frame

A

Often sampling units of a population are individually named or numbered to form a list called a sampling frame

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13
Q

What is a parameter

A

A number that describes the entire population

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14
Q

What is a statistic

A

A number taken from a single sample - you can use one or more of these to estimate the parameter

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15
Q

What is continuous data

A

Data which can take any value in a given range (you measure it and round it)

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16
Q

What is discrete data

A

Only takes specific values in a given range (you often count it)

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17
Q

What is qualitative data

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A

Data associated with non- numerical observations

18
Q

What is quantitative data

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A
  • Data associated with numerical observations
  • can be either discrete of continuous
19
Q

What is random sampling

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A
  • Where every member of the population has an equal chance of being selected
  • the sample should therefore be representative of the population
  • random sampling helps to remove bias from a sample
20
Q

What are the three methods of random sampling

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A
  • simple random sampling
  • systematic sampling
  • stratified sampling
21
Q

What is simple random sampling

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A
  • where every sample of size n has an equal chance of being selected
  • need a sampling frame
  • each sample is allocated a unique number and a selection of the number are chosen at random
22
Q

What are the two methods of choosing the numbers in simple random sampling

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A
  • lottery sampling - where the members of the sampling frame are written and placed in a ‘hat’ and requires tickets to be drawn out
  • generating random numbers using a computer or calculator
23
Q

What are the advantages of simple random sampling

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A
  • a fair way to select a sample
  • the sample is probably representative of the population
  • each sampling unit has the same chance of being chosen - not bias
24
Q

What are the disadvantages of simple random sampling

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A
  • Not possible without a sampling frame
  • potentially time consuming, disruptive and expensive when the population is large
  • minority groups might be missed
25
What is systematic sampling
- when you choose a starting point at random then sytematically select objects a certain number apart - e.g. for a population of 200 and a sample of 50 : 200/50 = 4 - choose a random stating point from person 1 - 4 then select every 4th member till 50 samples - only random IF the sampling frame has NO ORDER to it (no alphabetical order)
26
What are advantages of systematic sampling
- can be quick and easy to use - suitable for large samples and large populations
27
What are disadvantages to systematic sampling
- not possible without a sampling frame - if the sampling technique coincides with a periodic trait in the population, the sampling is no longer representative, introduces bias - there may be missing values - minority groups might be missed
28
What is stratified sampling
- when the population is split into distinguishable groups which covers the whole population - the groups are called stratas - the frequencies for each group in the sample are proportional to the frequencies for each group in the population - e.g. population is 100 F 200 M to select proportional stratifies sample of 50 do F = 100/300 x 50 M = 200/300 x 50
29
What are the advantages of stratified sampling
- minimises sample selection bias by ensuring certain segments of the population are not overrepresented or under - the frequencies for each strata can be proportional to the frequencies for each group in the population - minor groups get included - sample reflects the population
30
What are the disadvantages of stratified sampling
- not possible without a sampling frame - strata must e carefully defined - sometimes difficult to split the population into naturally occurring groups
31
How do you pick a sampling method
- consider whether or not you can list every member of a population - identify any sources of bias and any difficulties you might face in taking certain samples - compare the different sampling methods you have available and choose the one that best suits your needs and limitations
32
What is bias
A sampling method is biased if it creates a sample that does not represent the population
33
What are the types of non-random sampling
- opportunity sampling - quota sampling
34
What is opportunity sampling
- most used by social science researchers - taking samples from target population who are available at the time and in the right criteria - e.g. first 10 people outside shops carrying shopping bags
35
What are the advantages to opportunity sampling
- easy to select the sample - inexpensive
36
What are the disadvantages to opportunity sampling
- unlikely to produce a sample representative of the population - highly dependent on the individual researcher (nice to interview) - means data collected can become biased
37
What is quota sampling
- when the population is split into groups or strata as for stratified sampling - the size of each group determines the proportion of the sample that should have that characteristic - then a judgement is used to select the members from each group - interviewer meets, assesses groups, allocates - continues until quota are filled - ignores sample if quota’s full or sample ignores
38
What are the advantages to quota sampling
- even a small sample will still be representative of the population - does not need a sampling frame - quick, easy, inexpensive - different group’s responses can be compared
39
What are the disadvantages of quota sampling
- non- random, so could be biased - the population must have been split into groups, which could be inaccurate, time consuming and difficult - non-responses aren’t recorded as such, which might distort the interpretation
40
What is the difference between stratified and quota sampling
- both methods parts the population into mutually exclusive sub-groups - stratified - everyone has an equal chance of selection (random method) - quota - down to the interviewer which means the sample can become more bias - equal chance of being picked is reduced

Maths (2 decks)

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