Sample Size & Power Calculation Help
Students & Researchers
What is Sample Size?
Sample size refers to the number of subjects
participants studied in a trial, including the treatment and control groups, where
applicable. Sample size refers to the specific size of the group or groups being
studied in your research. The intended sample size is the number of participants
planned to be included in your study. This number is not arbitrary and sample
size is usually determined by using a power analysis.
The sample size should be adequate to provide a high probability of detecting as
significant an effect size of a given magnitude if such an effect actually
Once you have conducted a power analysis you will know the exact sample
size needed for your study. The achieved sample size is the number of
participants that are actually enrolled in or complete the study. Generally, the
larger the sample size, the more reliable the study results are, and the more
likely it is that the results can be generalized to other people.
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Why Calculating Sample Size is Important
A power analysis can help you determine how large
of a sample you need to make accurate statistical conclusions. To determine if a
statistical test will have adequate power, analyses to calculate how large of a
sample is required must be conducted before you begin your study. Sample size
calculation can provide you with the appropriate number of participants you will
need to address your research question properly.
Determining sample size is a very important issue because samples that are too
large may waste time, resources and money, while samples that are too small may
lead to inaccurate results. Without a power analysis, you will not know if your
proposed sample size is too large or too small.
A sample size that is too small
will not allow you to properly address your research questions with your
proposed statistical analysis. A sample size that is too large will cause you to
waste important time or financial resources. To avoid either of these scenarios,
you must conduct a power analysis. Calculating sample size can help you
determine the ability of your study to detect any effects. We can conduct your power analysis for you to determine the
sample size needed to adequately address your research question using the
appropriate statistical test(s). This information is important for any study and
can save you valuable resources and time.
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How to Determine Sample Size
Sample size is generally calculated with a power analysis. To calculate your
sample size you will need certain information. The information needed to
calculate sample size will depend on the statistical test you plan to use.
Irrespective of the statistical test you plan to use in your study, you will
need to know the desirable effect size to determine sample size. Remember that
it takes huge samples to detect tiny differences but tiny samples to detect huge
differences, so you have to specify the size of the effect you are trying to
detect. You will also need to know the alpha level you want to use for the
statistical test (e.g. alpha=.05) to determine sample size. If you plan to use
regression analysis in your study you will need to know the number of predictors
that will be included in your regression model to calculate sample size.
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Help You Calculate Sample Size
We recommend consulting with someone who is knowledgeable about sample size
calculation and who can explain the various components of conducting a power
analysis. Sample size calculation
will also vary depending on the type of statistical test you are using.
Given the importance of determining sample size, it is important that sample
size calculations are conducted properly. If you are unsure about the steps mentioned,
then let us help you calculate your study's sample size. We
can also help you decide which statistical tests to choose for your study.