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A-level Maths > stats > Flashcards

Flashcards in stats Deck (20):
1

sample

set of data values for a random variable

2

population

a group that you want to sample information about.

3

sampling frame

a collection of the items available to be sampled

4

sample survey

when information is collected from a small representation of the population

5

sampling unit

the person/object to be sampled

6

sampling fraction

the proportion of available sampling units that are actually sampled

7

census

when all the population has information collected about them

8

simple random sampling

every item in a population has an equal chance of being chosen. each item is assigned an ID and a random number table/generator is used to chose a random sample of numbers. suited to a small population.

9

opportunity/convenience sampling

sampling due an easy opportunity. leads to bias and an unrepresentative sample however useful for initial studies

10

stratified sampling

the population is divided into categories then a random sample is chosen from each category.
each categories size is proportional with the population.

11

cluster sampling

the population is divided into strata representative of the population. a random sample of clusters is chosen and every item in the chosen clusters is sampled.

a large number of small clusters is most accurate.

12

systematic sampling

a simple rule/pattern is used to chose the sample. Every item in the sampling frame is listed and every nth term is selected.

simple and quick but may be unrepresentative if a pattern exists in the list

13

quota sampling

the population is divided into groups and a given number from each group is sampled.

cheap and quick

14

self-selecting sample

where people volunteer to taake part or are given a choice to participate.

may be bias as people may chose to express their opinions of certain matters.

15

unimodal

one bump

16

bimodal

two bumps

17

positively skewed

bump near beginning

18

negatively skewed

bump near end

19

median

n+1/2

20

frequency density

= frequency/ class width