A hypothesis test for statistical power will help detect the probability of an effect. You can only spot the true effect if available. With confidence in the conclusion from the study’s outcome, you can calculate and report the power after completing the experiment. The analysis is an imperative tool to evaluate the sample size and the number of observations. This can help detect the effect in the experiment. In the following sections, you will understand how the power analysis is the hypothesis test’s essence. So let’s begin:
The researcher conducts the power analysis before data collection. The analysis aims to support researchers in determining the smallest sample size. The sample size is suitable for evaluating the test’s effect on the preferred satisfaction level. The smaller samples are less expensive compared to the larger samples. Therefore, researchers prefer power analysis for the probability of the effect. Another benefit of depending on the smaller samples is the optimization of the significance testing.
Power analysis interlinks with the tests of hypotheses. During the test researcher commits two types of errors:
- Type I error
- Type II error
Researchers should note that with larger sample sizes, they can easily achieve the 0.05 significance level. On the other hand, if the sample is very small, the investigator might require a Type II error because of the deficient power.
Factors Affecting the Power Analysis
You might think that the effect size and the subject’s number are imperative factors of the power analysis. Even though the effect size is the main contributor to power, there are numerous other factors that affect the power of a study. Below we will discuss the mechanical and the methodological issues affecting the power:
The first factor in increasing power is through the alpha level. While performing the pilot study, this strategy is effective. However, it can be non-viable to increase the alpha level. Researchers are now considering alpha level as 0.1 instead of 0.05. The reduction in the levels will affect the power and contribute to providing relevant results.
Sample size will also contribute to increasing power. Increasing the number of subjects will provide a variety of samples with different restrictions. This is understandable that all the groups should include equal sample numbers, but it is not quite necessary. For instance, it is funding an interview of 50 cancer survivors or accessing 20 autistic children. You can increase the subjects for a better outcome. However, increasing the sample size has a diminishing return effect in the control group.
Increasing the effect size will also increase the power. You can utilize experimental manipulation for the increment. However, this technique is effective in increasing the alpha level, but in various situations such as increasing the dose of the medication, it does not make any sense. If that’s the case, you can use another technique to increase the effect size and generate powerful statistical analysis.
If you cannot change the experimental manipulation, you can make changes in the experimental tasks. When you utilize the number of tasks in your research, you can choose from the best task providing maximum power. Not sure about what tasks you can review? You can also design sensitive tasks according to your research project.
The process to measure the response variable is also important. Using low measurement error and high sensitivity techniques will help you measure the power. Researchers have numerous measures to choose from. For instance, you will find the number of measures in attitudes, IQ, and anxiety. By manipulating the measures, you can reduce the measurement error.
Various types of experimental designs have different power than one another. For instance, repeated measures designs are powerful and provide instant results. You can increase the power by increasing the repeated measures designs during power analysis. This technique has diminishing returns by collecting many time points.
The number and types of groups will also affect the outcome of the power analysis. You can reduce the number of subjects by reducing the number of experimental conditions. Also, you can add more groups but keep the same number of subjects. When you perform power analysis, you should identify how many subjects to add for detecting the effect efficiently.
When there is a disruption in the assumptions of the test, you can make certain changes. Specifically, you can change the type of procedure in order to increase the power. After the violation of the assumption, you will not find the powerful outcome of the test. Violations of assumptions such as normality, independence, and heterogeneity will reduce the power. In such cases, you should use nonparametric alternatives, increasing the power.
Modification of the statistical model is also possible. Changing the main effects instead of others will increase power. Therefore, you need to find if the main effect of the model is powerful enough. If the power is not sufficient, you can add more interactions. Before determining the subject, you should also check if the power analysis programs include interaction terms or not.
Modify Response Variable
Other than changing the statistical model, try modifying the response variable. This modification will be beneficial for meeting the assumptions while reducing the extreme score of the statistical procedure. However, you need to be careful, as transforming the variables will increase the difficulty level while interpreting.
Purpose of the Study
The reasons to conduct the research are also crucial while performing power analysis. Some researchers are replicating previous research; others determine the difference of coefficient from zero. The purpose of the study affects the sample size. Instead of sampling the research error, experts will assign the casual reasons and differentiate between various researches.
When you are conducting research, you will encounter missing data issues. If you want to increase the power, you need to reduce the missing data. Try to attribute few minus data points on few variables. You can also remove the complete dataset to deal with the missing data problem.
When you conduct power research, consider different factors affecting the output of your research. You need to analyze the process and estimate the result for accountability. Focus on adjusting the number of subjects, alpha level, and the size of the samples. Try to collect the data and experiment with the variables to increase the power. You can change the factors depending upon the requirements and accuracy of the model. In simple words, power analysis is the planning to make the model efficient and test the hypothesis.