SECTION 11- DATA PRESENTATION AND INTERPRETATION

Question 1

what is meant by the term population

Answer 1

• it’s all the individuals/ set of individuals you’re interested in for a particular investigation
• can be difficult to investigate an entire population, so you could choose a sample

Question 2

what is simple random sampling

Answer 2

• items in sample are chosen by random e.g. using a random number generator
• every possible sample has the same probability of being selected

Question 3

advantages and disadvantages of simple random sampling

Answer 3

Advantages:
- everyone has a chance of being selected
Disadvantages:
- won’t always be possible, because you might not have a list of every member of the population

Question 4

what is cluster sampling

Answer 4

• if the population is divided into subgroups which are reasonably representative of the entire population
• so cluster sampling means taking the sample from a few of these subgroups e.g. if you want to take a of Yr11 students, you might take a sample from 2 or 3 different schools

Question 5

what is opportunity sampling

Answer 5

• when individuals are chosen to be part of a sample as opportunity rises e.g. interviewing passer-bys on the street

Question 6

what is stratified sampling

Answer 6

• when the parent population is divided into subgroups (or strata) like by age or gender
• stratified sampling ensures that all strata are sampled – subgroups aren’t expected to be a representation of the population
• if numbers sampled from each strata are proportional to size of the strata – this is proportional stratified sampling

Question 7

what is quota sampling

Answer 7

• similar to a stratified sample
• but the number of data items in each stratum are specified e.g. certain no. of males and females may be required
• method used by interviewers and selection of sample members is up to interviewer

Question 8

what is a self-selected sample

Answer 8

• individuals in the sample have chosen to be in the sample e.g. the respondents to a survey posted publicly on the Internet

Question 9

what is systematic sampling

Answer 9

• choosing individuals to form a sample e.g. the parent population was all the Yr11 students in a school – you might obtain an alphabetical list and select every other student on the list

Question 10

examples of samples prone to bias

Answer 10

Opportunity sampling:
- if you survey passer-bys in the middle of the street on working days – sample may include a disproportionate no. of retired people
Self-selected sample:
- when posting a survey on a website, the visitors might not be a representative of the population as a whole or they might already hold a strong opinion about the subject of the survey

Question 11

equation for combing means

Answer 11

mean = total / number so to find total it’s mean x n

- to combine means it’s the total(1) + total(2)/ n(1) + n(2)

Question 12

when is interpolation used

Answer 12

• to calculate the median and quartiles of grouped data

Question 13

how to work out the median in grouped data when there are gaps

Answer 13

• assume numbers have been rounded to nearest whole number, so change them so there’s no gap e.g 21- 25 becomes 20.5- 25.5
• then calculate the cumulative freq. and find the median

Question 14

calculating the median (in interpolation)

Answer 14

lower class boundary + (how many in/ group total) x class

Question 15

advantages and disadvantage of quota sampling

Answer 15

ADVANTAGES:
- cost effective and is easy to conduct
DISADVANTAGES:
- doesn’t allow random selection of participants, so won’t be accurate
- can be biased as individuals chosen is up to interviewer (may choose people more co-operative)

Question 16

how to calculate the variance (σ²)

Answer 16

mean of the squares - square of the mean

Question 17

how to calculate the standard deviation (σ)

Answer 17

• it’s the square root of the variance

Question 18

what does the area in a histogram represent

Answer 18

frequency

Question 19

what is bivariate data

Answer 19

• data that has pairs of values for two variable

- it can be represented on scatter diagrams

Question 20

how to plot on a scatter diagram

Answer 20

• independent variable (something researcher can control) is plotted on the x-axis
• dependent variable (something measured by researcher) is plotted on the y-axis

Question 21

difference between negative and positive correlation

Answer 21

• negative correlation is when one variable decreases when the other increases
• positive correlation is when one variable increases with the increase of the other variable (both variables are increasing)

Question 22

what is a casual relationship (between variables)

Answer 22

• when a change in one variable causes a change in the other

Question 23

what is standard deviation

Answer 23

finding out how far away the numbers are from the mean

Question 24

what is uniform distribution

Answer 24

• when all the outcomes are equally likely

Question 25

what are measures of central tendency (and examples)

Answer 25

• it helps you find the middle/ average of a data set e.g. mean, mode and median

Question 26

how to calculate the mean in a cumulative freq. table

Answer 26

sum of the products of the data values and their frequencies/ the sum of frequencies

Question 27

why is the mean good and bad for quantitative data

Answer 27

• it uses all values in the data, so it gives a true measure of data, but it’s affected by extreme values

Question 28

what are percentiles

Answer 28

• they split the data into 100 parts e.g. 10th percentile is 1/10 of the way through the data

Question 29

what is interpolation

Answer 29

• estimating unknown values that fall between known values

Question 30

examples of measures of spread

Answer 30

• range
• interquartile range
• interpercentile range
• variance

Question 31

finding outliers general formula

Answer 31

If it’s …
Greater than: Q₃ + k(Q₃ - Q₁)
Less than: Q₁ -k(Q₃ - Q₁)
(K WILL BE GIVEN IN THE EXAM – exam may have different ways of identifying outliers, so will be told what method to use)

Question 32

what is data cleaning

Answer 32

• process of removing anomalies from the data set, can do it by drawing box plots

Question 33

what is an outliers

Answer 33

• a value that falls either 1.5x interquartile range above the UQ or 1.5x interquartile range below LQ