at random
to represent the population
A random sample.
A sample that includes the population you are studying.
The main difference is that the way of selecting a sample Random sample purely on randomly selected sample,in random sample every objective has a an equal chance to get into sample but it may follow heterogeneous,to over come this problem we can use stratified Random Sample Here the difference is that random sample may follow heterogeneity and Stratified follows homogeneity
The main advantage is that the sample is representative of the population and the mean of the sample is an unbiased estimate of the population mean. Also, characteristics of other statistics based on the sample are well understood. However, sometimes it may not be possible to gather valid information from a sampling unit and then the sample is no longer random. This can be either because the sampling unit cannot be located or has been compromised by external factors. This can be particularly serious if the "missing" units share a common characteristic. Also, simple random samples may not include any units representing characteristics that are rare in the population - but important in the context of the experiment.
The sample size has no effect on the validity of an experiment: instead, it is the experimental procedure and integrity of the experimenters.The sample size can affect conclusions that may be drawn from an experiment. The larger the sample is, the more reliable these conclusions are.
The sampling proportion may be used to scale up the results from a sample to that of the population. It is also used for designing stratified sampling.
When we think of the term "population," we usually think of people in our town, region, state or country and their respective characteristics such as gender, age, marital status, ethnic membership, religion and so forth. In statistics the term "population" takes on a slightly different meaning. The "population" in statistics includes all members of a defined group that we are studying or collecting information on for data driven decisions.A part of the population is called a sample. It is a proportion of the population, a slice of it, a part of it and all its characteristics. A sample is a scientifically drawn group that actually possesses the same characteristics as the population - if it is drawn randomly.(This may be hard for you to believe, but it is true!)
It is quite likely that the sample is not representative of the population and so while statistical conclusion may be valid for the sample, they may not apply to the population.
The bottom line is it would be wasteful and foolish to use the entire population when a sample, drawn scientifically, provides accuracy in representing your population of interest. Assessing all individuals may be impossible, impractical, expensive or even inaccurate.
If temperature is being used to verify that the urine came from the correct person the temperature of the sample is an indicator that the urine is/may not be a fresh/valid sample...if the temperature is lower than expected.
Most people take samples so that they may make estimates of parameters of interest: mean, variance, etc for the whole population. For such an estimate to have any validity the sample data must be assumed to represent a population distribution. Otherwise any conclusions based on the sample are valid only for the sample: hardly worth the effort!
Convenience sample
Suppose you have a population for which you want to measure some particular attribute. It may not be feasible or sensible to collect the information from each and every member of the population. In that case you can take a subset of members from the population - called a sample - and collect the relevant information for them. Provided that the sample meets certain statistical conditions, the measurements made for the sample will be good approximations for the characteristics of the whole population.
The sample mean may differ from the population mean, especially for small samples.
Irene is an in-Valid because she has a heart problem. People with conditions can't be risked into space because accidents may occur.
it's composition may be different from sample to sample.
That sample which consists of several portions.It may be pure or impure.It may be heterogeneous or homogeneous.
A conclusion or assertion would be considered to be scientifically valid if the data are accurate and the reasoning based on that data is, as far as we can tell, correctly reasoned. Science does not deal in absolute truth, which is why scientists prefer the term valid, which indicates that as far as we presently know, this statement is true, although new data and/or new reasoning may cause us to change our minds in the future.
The main difference is that the way of selecting a sample Random sample purely on randomly selected sample,in random sample every objective has a an equal chance to get into sample but it may follow heterogeneous,to over come this problem we can use stratified Random Sample Here the difference is that random sample may follow heterogeneity and Stratified follows homogeneity