Representative/random
When there is an equal chance for each member of the population to be selected for participation in a study, the sample is considered to be a random sample. This method helps ensure that the sample is representative of the population, reducing bias and allowing for more generalizable results. Random sampling is a fundamental principle in statistical research techniques.
Large samples can be just as biased as small samples, depending upon how they are selected. For example, you want to do a survey to see how popular the President is, but you only interview men, refusing to interview women. No matter how many men you interview, this bias still exists. A sample of a million men is still biased if you have excluded women. (Although the data are still significant as long as you recognize that the bias exists.)
One effective way to ensure that a sample is representative of the population is to use random sampling. This method involves selecting individuals from the population in such a way that every member has an equal chance of being chosen, thereby minimizing selection bias. Additionally, stratified sampling can be employed, where the population is divided into subgroups (strata) based on specific characteristics, and random samples are drawn from each stratum to reflect the population's diversity.
Reagent Blank : Take reagent and add deionised water (in place of sample to be tested). Now measure the OD at specific wavelength --> this OD is your reagent blank. Substract this OD from your test result (with sample) to avoid any false +ve effect due to colour of reagents itself.Sample Blank : Take sample and measure the OD without adding reagents --> this OD is your sample blank. Substract this OD from your test result to avoid any false +ve effect due to colour and turbidity of sample itself. As it is the fact that colour and turbidity of each sample would vary from one to another.So now it is clear that Reagent blank is used to avoid bias due to colour of reagents and Sample blank is used to avoid bias due to sample itself.
In statistics, "n-1" refers to the degrees of freedom used in the calculation of sample variance and sample standard deviation. When estimating variance from a sample rather than a whole population, we divide by n-1 (the sample size minus one) instead of n to account for the fact that we are using a sample to estimate a population parameter. This adjustment corrects for bias, making the sample variance an unbiased estimator of the population variance. It is known as Bessel's correction.
bias
it is non-random and prone to bias unrepresentative of target population
When there is an equal chance for each member of the population to be selected for participation in a study, the sample is considered to be a random sample. This method helps ensure that the sample is representative of the population, reducing bias and allowing for more generalizable results. Random sampling is a fundamental principle in statistical research techniques.
The standard deviation. There are many, and it's easy to construct one. The mean of a sample from a normal population is an unbiased estimator of the population mean. Let me call the sample mean xbar. If the sample size is n then n * xbar / ( n + 1 ) is a biased estimator of the mean with the property that its bias becomes smaller as the sample size rises.
Large samples can be just as biased as small samples, depending upon how they are selected. For example, you want to do a survey to see how popular the President is, but you only interview men, refusing to interview women. No matter how many men you interview, this bias still exists. A sample of a million men is still biased if you have excluded women. (Although the data are still significant as long as you recognize that the bias exists.)
What? Bias is a one sided opinion
A biased survey is one that produces results that are systematically skewed due to flaws in its design, methodology, or execution. This bias can arise from various factors, such as leading questions, unrepresentative sample selection, or the way responses are collected. As a result, the findings may not accurately reflect the true opinions or behaviors of the target population, undermining the survey's validity. It is crucial to minimize bias to ensure reliable and generalizable results.
Bias
One effective way to ensure that a sample is representative of the population is to use random sampling. This method involves selecting individuals from the population in such a way that every member has an equal chance of being chosen, thereby minimizing selection bias. Additionally, stratified sampling can be employed, where the population is divided into subgroups (strata) based on specific characteristics, and random samples are drawn from each stratum to reflect the population's diversity.
One potential bias of the Dunedin Multidisciplinary Health and Development Study is selection bias, as participants were chosen from a specific population. Another potential bias could be attrition bias, as participants may drop out of the study over time, affecting the representativeness of the sample. Additionally, there may be response bias in self-reported data, where participants may not provide accurate information.
To ensure an experiment is a fair test, it is essential to control variables by keeping all conditions the same except for the one being tested (the independent variable). Replication of the experiment helps confirm results by reducing the impact of random errors. Random assignment of subjects can also help eliminate bias. Additionally, using a sufficient sample size increases the reliability of the results.
Reagent Blank : Take reagent and add deionised water (in place of sample to be tested). Now measure the OD at specific wavelength --> this OD is your reagent blank. Substract this OD from your test result (with sample) to avoid any false +ve effect due to colour of reagents itself.Sample Blank : Take sample and measure the OD without adding reagents --> this OD is your sample blank. Substract this OD from your test result to avoid any false +ve effect due to colour and turbidity of sample itself. As it is the fact that colour and turbidity of each sample would vary from one to another.So now it is clear that Reagent blank is used to avoid bias due to colour of reagents and Sample blank is used to avoid bias due to sample itself.