Sample Size Calculator

Sample size calculator is an important tool used in statistics and research to determine the appropriate sample size required to ensure the accuracy and reliability of study results.

Importance of Sample Size in Research:

The sample size is an important consideration in research because it affects the accuracy and reliability of the study results.

• A larger sample size generally provides more reliable and accurate results, as it reduces the margin of error and increases the statistical power of the study. 
• A small sample size may lead to biased or inconclusive results.

For example, a researcher wants to conduct a study to determine how common a certain disease is in a population. A small sample size in a disease prevalence study may not be representative of the actual rate in the population, while a larger sample size improves accuracy and representation.

Sample Size Formula for Surveys and polls:

One commonly used formula for calculating sample size in surveys and polls is:

n = {z² * p * (1 – p)} / m²

Where:

• n = sample size
• z = z-score corresponding to the desired level of confidence (e.g., 1.96 for 95% confidence)
• p = proportion or percentage estimate of the population that is expected to have the characteristic of interest
• E = margin of error as a decimal (e.g., 0.03 for 3%)

Factors Affecting Sample Size:

Several factors can affect the sample size required for a study. These factors include:

Population size: The size of the population from which the sample is drawn affects the sample size. A larger population size requires a larger sample size to achieve a representative sample.

Confidence level: The level of confidence or the degree of certainty desired by the researcher also affects the sample size. A higher level of confidence requires a larger sample size to reduce the margin of error.

Margin of error: The margin of error is the range within which the true value of a parameter is expected to fall. A smaller margin of error requires a larger sample size.

Variability: The variability or the range of values within the population also affects the sample size. A larger variability requires a larger sample size to achieve a representative sample.

Effect size: The effect size refers to the magnitude of the difference between the groups being studied. A larger effect size requires a smaller sample size to detect a significant difference.

How to calculate sample size?

Example

If a researcher wants to conduct a survey with a 95% confidence level and a margin of error of 3%, and estimates that 50% of the population will have the characteristic of interest, the sample size would be calculated as:

Solution:

Confidence level = 95%

Margin of error = 3%

Population = 50%

By putting values in the above formula

n = (1.96)² * 0.5 * (1 - 0.5)) / (0.03)²

n = 1068.44 (rounded up to 1069)