Statistics

Populations and Samples:

• A population is the _____ ____ of items that are of interest

• A census observes or ________ ______ _________ of a population

• A sample is a _______of ________ taken from a _____of the population which is used to find out information about the population as a _____.

• Individual units of a population are known as ________ ____. 

• Sampling units are named or numbered individually to form a ______ ____. 

whole set, measures every member, selection, observations, subset, whole, sampling units, sampling frame

Advantages and Disadvantages of censuses and samples:

Census

• Advantages: It should give completely ______results

• Disadvantages: Time consuming and expensive; cannot be used when the testing process _______the item

Sample

• Advantages: Fewer people have to respond than in a census, so it is more time and money efficient

• Disadvantages: The data may not be as accurate as a census; the sample may not be large enough to give information about small ________ of the population 

accurate, destroys, sub-groups

More on Sampling:

• A larger sample is more accurate but requires more resources.  

• If a population is varied, you need a larger sample than if the population were ______. 

• Different samples can lead to different conclusions  due to the ______ _________ in a population. 

uniform, natural variations

Random Sampling

• A simple random sample of size n is when every sample __ _____n has an equal chance of being selected. Simple random sampling requires a random number generator or ______

• In systematic sampling, the required elements are chosen at regular intervals from an ordered list. The first _______should be chosen at _____. 

• In stratified sampling, the population is divided into ______ _______ ____, and a random sample is taken from each. The number sampled in a stratum = (number in stratum / number in population) x overall sample size

of size, lottery, element, random, mutually exclusive strata

Simple Random Sampling

Advantages

• Free of bias

• Easy and cheap to implement for small populations and small samples

• Each sampling unit has a known and equal chance of selection

Disadvantages

• If population size is large, than could be time and money consuming, as well as ________

• A ______ ______is needed

disruptive, sample frame

Systematic Sampling

Advantages

• Simple and quick to use

• Suitable for large samples and population s

Disadvantages

• A sampling frame is needed

• Bias may be introduced if the sampling frame is not ______

random

Stratified Sampling

Advantages

• Sample accurately reflects the population structure

• Guarantees proportional representation of groups within a population

Disadvantages

• Population must be clearly classified into distinct strata

• Selection within each stratum suffers from the ____ disadvantages as simple random sampling

same

Non-random Sampling—Opportunity Sampling:

• Opportunity sampling, also known as _________sampling, consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Advantages

• Easy to carry out

• Inexpensive

Disadvantages

• Unlikely to provide a _______sample

• Highly _______on _______ _________

convenience, representative, dependent, individual reseracher 

Non-random Sample—Quota Sampling:

Advantages

• Allows a small sample to still be representative of the population

• No sampling frame required

• Quick, easy and inexpensive

• Allows for easy _______between different groups within a population

Disadvantages

• Non-random sampling can introduce ____

• Dividing the population into groups can be costly or inaccurate

• _________are not recorded as such

comparison, bias, non-responses

Non-random Sample—Quota Sampling:

• In quota sampling, an interview or researcher selects a sample that _____the characteristics of the whole population

• First, divide the population into groups according to given characteristics.

• The size of each group determines the ________of the sample that should have that characteristic.

• The interviewer should assess which groups people fall into, as part of the interview.

• Once a quota has been filled, __ more people in that group are interviewed.

reflects, proportion, no 

Types of Data

• A value that can take ____ value in a given range is a continuous variable

• A value that can take only _____ values in a given range is called a discrete variable.

any, specific