AS Statistics

Question 1

Population

Answer 1

The whole set of items that are of interest

Question 2

Census

Answer 2

Observes or measures every member of a population

Question 3

Sample

Answer 3

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

Question 4

Sampling frame

Answer 4

List of sampling units, with each unit given an identifying name or number

Question 5

Advantages/disadvantages of a census

Answer 5

Advantages:
Completely accurate result
Disadvantages:
Time consuming, expensive, cannot be used when testing process destroys the item, hard to process large quantity of data

Question 6

Sample advantages/ disadvantages

Answer 6

Advantages:
Less time consuming/expensive, fewer people have to respond, less data to process than in a census
Disadvantages:
Data may not be as accurate, sample may not be large enough to give data about small subgroups of the population

Question 7

Sampling units

Answer 7

Individual units of a population

Question 8

Simple random sample

Answer 8

Where every sample of size n has an equal chance of being selected

Question 9

Systematic sampling

Answer 9

Required elements are chosen at regular intervals from an ordered list

Question 10

Stratified sampling

Answer 10

Population is divided into mutually exclusive strata and a random sample is taken from each

Question 11

Simple random sampling advantages/disadvantages

Answer 11

Advantages: free of bias, easy and cheap to implement for small samples/populations, each sampling unit has a known and equal chance of selection
Disadvantages: not suitable for large populations (time consuming, disruptive, expensive), a sampling frame is needed

Question 12

Systematic sampling advantages/disadvantages

Answer 12

Advantages: simple and quick to use, suitable for large samples/populations
Disadvantages: a sampling frame is needed, can introduce bias if the sampling frame is not random

Question 13

Stratified sampling advantages/disadvantages

Answer 13

Advantages: sample accurately reflects population structure, guarantees proportional representation of groups within a population.
Disadvantages: population must be classified into distinct strata, selection within each stratum suffers from same disadvantages as simple random sampling

Question 14

Quota sampling

Answer 14

an interviewer or researcher selects a sample that reflects the characteristics of the whole population

Question 15

Opportunity sampling

Answer 15

Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for

Question 16

Quota sampling advantages/disadvantages

Answer 16

Advantages: allows a small sample to still be representative of the whole population, no sampling frame required, quick, easy and inexpensive, allows for easy comparison between different groups within a population
Disadvantages: non-random sampling can introduce bias, population must be divided into groups which can be costly and inaccurate, increasing scope of study increases number of groups (adding time and expense), non-responses are not recorded as such

Question 17

Opportunity sampling advantages/disadvantages

Answer 17

Advantages: easy to carry out, inexpensive
Disadvantages: unlikely to provide a representative sample, highly dependent on individual researcher

Question 18

Quantitative data/variables

Answer 18

variables or data associated with numerical observations

Question 19

Qualitative data/variables

Answer 19

variables or data associated with non-numerical observations

Question 20

continuous variable

Answer 20

a variable that can take any value in a given range

Question 21

discrete variable

Answer 21

a variable that can take only specific values in a given range

Question 22

grouped frequency table (gft)

Answer 22

the specific data values are not shown but are included in groups (or classes)

Question 23

mid-point (gft)

Answer 23

average of class boundaries

Question 24

Daily mean temperature units

Answer 24

degrees Celsius

Question 25

Daily total rainfall units

Answer 25

mm | Amounts less than 0.05 mm are recorded as 'tr' or 'trace'

Question 26

Daily total sunshine

Answer 26

recorded to the nearest tenth of an hour

Question 27

Daily mean windspeed/daily maximum gust units

Answer 27

knots

Question 28

Daily maximum relative humidity

Answer 28

Given as a percentage of air saturation with water vapour. | Above 95% gives rise to misty and foggy conditions

Question 29

Daily mean cloud cover units

Answer 29

'okras' (eighths of the sky covered by cloud)

Question 30

Daily mean visibility units

Answer 30

decametres (Dm)

Question 31

Daily mean pressure units

Answer 31

hectopascals (hPa)

Question 32

measure of location

Answer 32

a single value which describes a position in a data set

Question 33

Measure of central tendency

Answer 33

a single value which describes the centre of the data

Question 34

Mode/modal class

Answer 34

the value or class that occurs most often

Question 35

Median

Answer 35

the middle value when the data values are put in order

Question 36

Mean formula

Answer 36

sum of the values/number of values

Question 37

Lower quartile

Answer 37

one-quarter of the way through the data set

Question 38

Upper quartile

Answer 38

three-quarters of the way through the data set

Question 39

Range

Answer 39

difference between the largest and smallest values in the data set

Question 40

Interquartile range (IQR)

Answer 40

the difference between the upper and lower quartiles

Question 41

Interpercentile range

Answer 41

the difference between the values for two given percentiles

Question 42

Standard deviation

Answer 42

square root of the variance

Question 43

Coding

Answer 43

a way of simplifying statistical calculations

Question 44

Outlier

Answer 44

an extreme value that lies outside the overall pattern of the data

Question 45

Outlier common definition

Answer 45

Greater than Q3 + k(IQR) | Or less than Q1 - k(IQR)

Question 46

cleaning the data

Answer 46

the process of removing anomalies from the data

Question 47

anomalies

Answer 47

when an outlier should be removed from the data because it is clearly an error and misleading.

Question 48

frequency polygon

Answer 48

When the middle of the top of each bar in a histogram is is joined with a straight line

Question 49

frequency density equation

Answer 49

frequency/class width

Question 50

Bivariate data

Answer 50

data which has pairs of values for two variables

Question 51

Independent/explanatory variable

Answer 51

the variable controlled by the researcher (x-axis)

Question 52

Dependent/response variable

Answer 52

the variable measured by the researcher (y-axis)

Question 53

correlation

Answer 53

describes the nature of the liner relationship between two variables

Question 54

causal relationship

Answer 54

when a change in one variable causes a change in the other (Correlation does not mean causation!) You need to use context of question and common sense to determine this

Question 55

experiment

Answer 55

a repeatable process that gives rise to a number of outcomes

Question 56

event

Answer 56

a collection of one or more outcomes

Question 57

sample space

Answer 57

the set of all possible outcomes

Question 58

mutually exclusive

Answer 58

when events have no outcomes in common

Question 59

Addition rule (probability)

Answer 59

For mutually exclusive events: | P(A or B) = P(A) + P(B)

Question 60

Independent

Answer 60

when one event has no effect on another

Question 61

Multiplication rule (probability)

Answer 61

P(A and B) = P(A) x P(B)

Question 62

tree diagram

Answer 62

can be used to show the outcomes of two or more events happening in succession

Question 63

random variable

Answer 63

a variable whose value depends on the outcome of a random event

Question 64

Sample space

Answer 64

the range of values that a random variable can take

Question 65

probability distribution

Answer 65

fully describes the probability of any outcome in the sample space

Question 66

discrete uniform distribution

Answer 66

when all of the probabilities are the same

Question 67

Sum of the probabilities of all outcomes of an event add up to 1

Answer 67

ΣP(X=x) = 1

Question 68

test statistic

Answer 68

the result fo the experiment or the statistic that is calculated

Question 69

null hypothesis, H0

Answer 69

the one you assume to be correct

Question 70

alternative hypothesis, H1

Answer 70

tells you about the parameter if your assumption is wrong

Question 71

critical region

Answer 71

region of the probability distribution which, if the test statistic falls within it, would cause you to reject the null hypothesis

Question 72

critical value

Answer 72

first value to fall inside the critical region

Question 73

actual significance level

Answer 73

probability of incorrectly rejecting the null hypothesis