statistics: data collection?0

what is a population?

• the whole set of items that are of interest

what is raw data?

• information obtained from a population

what is a sample?

• a selection of observations taken from a subset of population and is used to find out more information about the population as a whole

what is a census?

• it measures or observes every member of a population

advantages and disadvantages of a census?

• advantages: results should be completely accurate

• disadvantages: time consuming and expensive; hard to process large quantity of data

advantages and disadvantages of sample?

• advantages: less time consuming and cheaper; less people have to respond; less data needs to be processed

• disadvantages: data may not be as accurate; sample may not be large enough to give information about small subgroups of the population

what are sampling units?

• individual units of a population

what is a sampling frame?

• when sampling units are named and numbered to form a list

what is random sampling?

• each member of the population has an equal chance of being selected

• the sample should be representative of the population and the bias should be removed

what are the 3 types of random sampling?

• simple random sampling

• stratified sampling

• systematic sampling

simple random sampling?

• a simple random sample size of n is one where every sample of size n has an equal chance of being selected

advantages of simple random sampling?

• free of bias

• easy and cheap for small samples and populations

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

disadvantages of simple random sampling?

• not suitable for large samples and populations

• sampling frame is needed

systematic sampling?

• the required elements are chosen at regular intervals from an ordered list

example of systematic: how to get a sample size of 20 from population of 100?

• 100 / 20 = 5, so every fifth person is chosen

• the first person is chosen at random

• if the first person chosen is 2, the remaining samples will be 7, 12, 17, etc

advantages of systematic sampling?

• simple and quick to use

• suitable for large samples and large populations

disadvantages of systematic sampling?

• a sampling frame is needed

• bias is introduced if sampling frame is not random

what is stratified sampling?

• the population is divided into mutually exclusive strata and a random sample is taken from each

• number sampled in each stratum = (number in stratum / number in population) x overall sample size

advantages of stratified sampling?

• sample accurately reflects population structure

• proportional representation of group within population

disadvantages of stratified sampling?

• population must be clearly classified into distinct strata

• same disadvantages as simple random sampling within each stratum

what are the 2 non-random sampling?

• quota sampling

• opportunity/convenience sampling

what is quota sampling?

• an interviewer or researcher selects a sample that reflects the characteristics of the whole population

advantages of quota sampling?

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

• no sampling frame required

• quick, easy and inexpensive

• easy comparison between different groups within a population

disadvantages of quota sampling?

• non-random sampling can introduce bias

• population must be divided into groups, which can be costly or inaccurate

• increasing scope of study increases number of groups, which adds time and expenses

• non-responses not recorded

what is opportunity/convenience sampling?

• sample is taken from people who are available at the time of study and who fits the criteria you are looking for

advantages of opportunity/convenience sampling?

• easy and inexpensive

disadvantages of opportunity/convenience sampling?

• unlikely to produce a representative result

• highly dependent of the individual researcher

what is quantitative data/variables?

• variables or data associated with numerical observations

what is qualitative variables/data?

• variables associated with non-numerical observations

what is a continuous variable?

• a variable that can take any value in a given range

what is a discrete variable?

• a variable that can only take specific values