Statistics Y1

Question 1

What is a census

Answer 1

When you sample every member of the population

Question 2

What is sampling error?

Answer 2

The difference between the estimate of a parameter from sample data compared to the true value

Question 3

What is one advantage of a census and one disadvantage

Answer 3

• the sample error is 0
  Often impractical or too costly

Question 4

Give 6 questions you can ask in order to check how valid the sample is?

Answer 4

1. is the data you are collecting relevant? (Are you asking the right questions to get the right answers?_
2. is the sample set likely to be biased? (This would introduce a systematic error)
3. Does the method of collection distort the data? Eg avoid leading questions
4. Is the right person collecting the data? (Bias can be introduced if people are likely to give a certain answer to a person in an authority position for example)
5. Is the sample large enough? (This depends how accurate you want the sample to be?)
6. Is the sampling procedure appropriate for the circumstances?

Question 5

What is simple random sampling?

Answer 5

• every member of the parent population is equally likely to be selected

Question 6

What is stratified sampling?

Answer 6

• put population into subgroups which are expected to have different characteristics
• subgroups are called strata
• sample all of the strata
  (Usually use simple random sampling within the stratum)

Question 7

What is proportional stratified sampling?

Answer 7

• the number sampled per strata is proportional to the size of the population of that strata

Question 8

What is systematic sampling? - what issue do you have to be aware of with this?

Answer 8

• choose the nth item every m items in a list
• be aware of cyclic patterns within the sampling frame

Question 9

What is quota sampling

Answer 9

• n number of a certain group must be sampled within the sample

Question 10

What is opportunity sampling and when is it useful

Answer 10

• when circumstances make a sample readily available and it is chosen on those grounds
• useful for an initial pilot study before a wider investigation takes place

Question 11

How do you find the median of n items

Answer 11

(n+1)/2

Question 12

The median is more formally called what

Answer 12

A measure of tendency

Question 13

What do Q1, Q2 and Q3 denote

Answer 13

Q1, the lower quartile
Q2, the median
Q3, upper quartile

Question 14

What percentile is Q1

Answer 14

25th percentile

Question 15

What % of data has values less than the 90th percentile

Answer 15

90%

Question 16

How do you display continuous grouped data which is found in frequency charts

Answer 16

Histograms

Question 17

Give 3 measures of central tendency

Answer 17

Mean, median, mode