Data:
- Data are values of qualitative (attributes) or quantitative (variable) from observations
- It is an abstract concept that can be viewed as the lowest level of abstraction, from which information and then knowledge are derived
Statistic:
- A statistic is a number that represents a property of the sample.
- The statistic is an estimate of a population parameter.
Parameter:
- A parameter is a numerical characteristic of the ==whole Population== that can be estimated by a statistic.
An attribute:
- a characteristic of an object which cannot be measured.
Variable:
- something that may or does vary which can be measured
- A discrete variable:
- a variable which can only take a countable number of values.
- Continuous variables:
Census vs Sample survey:
- Census refers to data collection about everyone or everything in a Population.
- This method gives a high degree of accuracy but is very expensive and time consuming.
- Sample survey:
- Only part of total population is used for collecting data.
- This method is less expensive than a census and the results can be obtained far more quickly.
- But the results have a degree of inaccuracy, depending on the sample size and methods for conducting survey.
Types of errors:
- is a sample selected in such a way that every item in the population has an equal chance of being included.
A sampling frame:
- is the source material from which a sample is drawn. It is a list of all those within a population who can be sampled.
- A sampling frame should have the following characteristics:
- Completeness
- Accuracy
- Up to date
- Non-duplication
- Drawbacks of random sampling:
- An unrepresentative sample may result.
- The members of population selected may be scattered over a wide area.
There are more sampling method
| Random sampling method | Desc |
|---|
| Simple random | All item has equal chance |
| Quasi-random | includes: Systematic, Stratified, and Multistage sampling |
| Systematic | pick every kth item where k=population size/sample size |
| Stratified | stratum sample size = (size of stratum)×(sample size)÷(size population) then use another method to selects elements from each stratum |
| Multistage | At each stage, a stratified random sample on a variable on which they could get information before sampling |
| Non-random sampling method | Desc |
|---|
| Quota | select a predetermined number or proportion of units with specific characteristics in a non-random manner |
| Cluster | the total population is divided into groups (or clusters) and a simple random sample of the groups is selected |
- Survey method: questionnaire and interview