Statistics - key Terms

Question 1

What is a population in sampling?

Answer 1

Is the whole set of items that are of interest

Question 2

What is a sample in sampling?

Answer 2

Some subset of the population intended to represent the population

Question 3

What is a sample unit in sampling?

Answer 3

Each individual thing in the population that can be sampled is known as a sampling unit. Often sampling units of a population are individually named or numbered to form a list called the sampling frame.

Question 4

What is data collected from the entire population known as in sampling?

Answer 4

Census

Question 5

What are advantages and disadvantages of using a census or sample in sampling?

Answer 5

Census
+ should give completely accurate result
- time consuming, can’t be used when testing involves destruction, large volume of data to process
Sample
+ cheaper, quicker, less data to process
- data may not be accurate, data may not be large enough to represent small sub-groups

Question 6

What are the 3 types of random sampling and what are the 2 types of non random sampling?

Answer 6

1. Simple random sampling
2. Systematic sampling
3. Stratified sampling
4. Quota sampling
5. Opportunity/convenience sampling

Question 7

What is simple random sampling, what is the method and what are +/- of it?

Answer 7

Every sample has an equal chance of being selected.
Method = In sampling frame, each item has identifying number. Use random number generator or ‘lottery sampling’ (name in hat) to select the items
+ bias free, easy, cheap, each number has known equal chance of being selected
- not suitable for large population size, sampling frame needed

Question 8

What is systematic sampling, what is the method and what are +/- of it?

Answer 8

Required elements are chosen at regular intervals in ordered list
Method - take every key elements where k=pop size (N) / samp size (n). Starting at a random item between 1 and k
+ simple, quick to use, suitable for large samples/populations
- sample frame needed, introduce bias if sampling frame isn’t random

Question 9

What is stratified sampling, what is the method and what are +/- of it?

Answer 9

Population divided into groups (strata) and a simple random sample carried out in each group.
Method - same proportions samp size (n) / pop size (N) sampled from each strata. Used when sample is large and population naturally divides into groups
+ reflects population structure, guarantees proportional representation of groups within population
- pop must be clearly classified into distinct strata, selection within each strata, suffer from same disadvantages as simple random sampling

Question 10

What is quota sampling, what is the method and what are +/- of it?

Answer 10

Population divided into groups according to characteristics. Quota if items/people in each group is set to try and reflect the group’s proportion in the whole pop, interviewee selects actual sampling units
+ small sample to still be representative of pop, no sampling frame, quick, easy, inexpensive, easy comparison between different groups in pop
- non random sampling can be bias, population must be divided into groups (costly or inaccurate), increasing scope of study increases number of groups (time, expense), non-responses are not recorded

Question 11

What is opportunity/convenience sampling, what is the method and what are +/- of it?

Answer 11

Sample taken from people who are availed at time of study, who meet criteria
+ easy, inexpensive
- unlikely to provide representative sample, highly dependent on individual researcher

Question 12

What is qualitative and quantitative data?

Answer 12

Qualitative = values that are always words or descriptions
E.g. favourite animal, month born
Quantitative = values that are always numbers (counted, measure on a scale)
E.g. favourite temperature, day born

Question 13

What is discrete and continuous data?

Answer 13

Discrete = Separated, limited to only limited quantitative variables
E.g. number of siblings, shoe size
Continuous = Joined together, unlimited quantitative variables
E.g. someone’s height, foot length

Question 14

What does mean, median, mode and range mean?

Answer 14

Mean = average of all numbers
Median = middle number in ascending order
Mode = most common number
Range = largest x smallest number

Question 15

What are measures of location, central tendency and spread?

Answer 15

Measures of location = single values that describe the position in a set of data
Measures of central tendency = to do with the centre of the data (e.g. notion of average)
Measures of spread = how spread the data is

Question 16

To work out mean from a data table

Answer 16

If whole number just use normal mean method
If has a class width, use the midpoint of the class width and multiply with frequency on a calculator table

Question 17

What is the rule for finding the position of the median?

Answer 17

n/2
If decimal answer, round up
If whole number, use half way between this value and the next one up
(E.g. 5 numbers, 5/2 = 2.5 rounds up to 3rd position, 4 numbers, 4/2 = 2, 2nd - 3rd position)