Sampling Flashcards
What is Random Sampling?
-Used to give every item in the population (the sampling frame) the same chance of being chosen. Each item is given a number, then numbers are picked at random, using either random number tables or a computer to identify the items to be measured or surveryed.
-Type of probability sampling.
What are the Advantages and Disadvantages of Random Sampling?
+Free from bias.
+Every member of the population has an equal chance of being chosen.
+Easy to implement.
-A complete list of the population may not be available.
-Minority subgroups within the population may not be present in sample (not representative of whole population).
-If the sampling frame is large, random sampling may be impractical and time consuming.
What is an Example of a Random Sampling?
Create a sampling frame by listing all the pupils a teacher teaches and giving each person an individual number between 1 and 300. Use the random number generator to generate 60 unique numbers between 1 and 300 (no repeats). Select the pupils corresponding to these number to be part of the sample.
What is Stratified Sampling?
-Used to ensure that each stratum (or layer) is properly represented in the sample. The population is divided into strata (layers) then a random sample from each stratum is selected using random sampling and all the selected items are surveryed
-Type of probability sampling.
What are the Advantages and Disadvantages of Startified Sampling?
+More accurate data.
+More manageable due to the subgroups.
+More representative.
-Requires more planning.
-Can’t be used in all studies.
-Tedious and time consuming.
What is an Example of Stratified Sampling?
In a college of 150 males and 250 females, a stratified sample of 80 students is to be selected to participate in a sruvey about transport. Since male students represent 150 of the college population of 400, then 250/400 of the sample of 80 should be male. 150/400 x 80 = 30, 30 males must be selected randomly. Therefore 50 females will also be selected randomly.
What is Systematic Sampling?
-Used to sample members from a larger population where the members are selected according to a random starting point but with a fixed, peridoic interval.
-Type of probability sampling.
What are the Advantages and Disadvantages of Systematic Sampling?
+Quick and cost effective.
+Low risk of bias.
+Easy to use and understand.
-Not strictly random, as some can’t be chosen once the starting point is decided.
-Greater risk of data manipulation as the researcher may be able to increase the likelihood of achieving a target outcome.
-Assumes the size of the population can be determined or can be reasonably approximated.
What is an Example of Systematic Sampling?
Create a sampling frame by listing all the pupils a teacher teaches and giving each person an individual number between 1 and 300. Do the calculation 300/60 = 5. Use the random number generator on a calculator to generate a number between 1 and 5. This generates the first person in the sample. Select every 5th person after the first person.
What is Cluster Sampling?
-Used often in market research. The popultation is divided into clusters (groups), then a sample of clusters is selected using random sampling and all items in those clusters are surveryed.
-Type of probability sampling.
What are the Advantages and Disadvantages of Cluster Sampling?
+Uses natural groupings
+Very cost and time effective compared to others like random.
+High reliability as the selected sample group will mirror similar characteristics of the population.
-Difficult to implement.
-Difficult to analyse.
-Not a genuine random sample as it can be subject to bias if only a few clusters are used, not whole population included.
What is an Example of Cluster Sampling?
The names of children aged 5-14, who attended school were known and 30 clusters were needed. The total population was divided by 30 to determine the sampling internal (a). Then a random number (n) was chosen and the school of the nth child in alphabetical order was the first cluster to be surveyed. The school of the (n+a)th child in alphabetical order was the second cluster surveyed. The school of the (n+2a)th child was the next and so on until 30 clusters (primary schools) were surveyed. If the same school is selected twice, then the school of the next child (n+a+1) on the list is substituted in its place.
What is Quota Smapling?
-Used in market research. The person doing the survey is told the quota (amount) of the items from each section to be surveyed and is then free to select those items as they wish.It relies on the non-random selection of a predetermined number or proportion of units, called a quota. You first divide the population into mutually exclusive subgroups (strata) and then recruit units until you reach you quota.
-Type of non-probability sampling.
What are the Advantages and Disadvantages of Quota Sampling?
+Simple to take.
+Time effective.
+Inexpensive.
-Not genuinely random since the surveyor picks the items and is likely to be bias.
-Not randomised as each person in one population does not have the same chance of being picked.
-It also means that it’s not possible to make statistical inferences, so may be hard to generalise.
What is an Example of Quota Sampling?
Divide the groups into mutually exclusive strat; year 7s, year9s and year 11,s. Do the calculations 120/300 x 60 = 24, 150/300 x 60 = 30, 30?300 x 60 = 6. Ask the first 24 year 7s that walk through the foor to be part of the sample. Ask the first class of year 9s that the teacher teaches the next week to be part of the sample.
