Estimation

Precision and confidence

Once the sample has been selected and the data has been collected, you have to calculate estimates for then population parameters. You can use the tools below the compute estimates for a population percentage and a population mean. To be able to do this, you must first enter the data.

Not only an estimate is computed, but also a confidence interval. This interval contains the true ppopulation level with a high probability. This high probability is called the confidence interval.

You have two options for the confidence level: 95% or 99%. Note that is relation between the confidence level of the confidence interval and the precision of the estimate:

• A choice for a higher confidence level (99%) will lead to a wider confidence interval, and thus to a less precise estimate.
• A choice for a lower confidence level (95%) will lead to a smaller confidence interval, and thus to a more precise estimate.

So you either draw a very precise conclusion with a lower level of confidence, or a less precision conclusion with a higher level of confidence.

The first step is to select the confidence level. There are two options: 95% or 99%:

 95% confidence level 99% confidence level

The next stop is to select the type of estimate you want to compute. There are two options: percentage or mean:

Estimating a percentage
To estimate a percentage you have to enter data in the input fields below. Note that all fields have to be filled in.

 Population size. If you don't know it, enter an estimate: The sample size: The sample percentage:

If you have entered all data, click on the button Compute below.

 Estimate of the population percentage: Standard error of the estimate: Lower bound of the confidence interval: Upper bound of the confidence interval: Confidence level:

Schatten van een gemiddelde

To estimate a percentage you have to enter data in the input fields below. Note that all fields have to be filled in.

 Population size. If you don't know it, enter an estimate: Enter the sample values of the variable. Click on Enter after each value.

If you have entered all data, click on the button Compute below. Click on the button Reset to compute another estimate.

 Sample size: Sum of the values: Sum of squares of the values:

 Estimate of the population mean: Standard error of the estimate: Lower bound of the confidence interval: Upper bound of the confidence interval: Betrouwbaarheid: