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Anova Two Factor with Replication [With Comparison]

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18th Sep, 2020
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Anova Two Factor with Replication [With Comparison]


Analysis of Variance or Anova, for short, is a technique of understanding the variance of variables. It makes it possible to calculate how much a particular variable affects the final result. Anova technique does this by eliminating or confirming the null hypothesis. A null hypothesis means that there exists no relationship at all between the two entities under observation. For example, if there are two variables A and B, we say that a null hypothesis between A and B holds if a change in A will not affect the results of B and vice-versa.

Before going into the details of Anova two-factor with replication, let us first discuss the basic concept of Anova.


Anova is a statistical concept, and no statistics holds without numbers. Anova requires a certain number through which it can analyze the null hypothesis that we pose at the start of the analysis. The three critical values for this calculation are F ratios and F-critical, with some significance values. Now here we will not go much into the detailed mathematical computation, but we will address the conceptual parts with examples.

The significance of a particular variable or entity is calculated by comparing the values with the overall impact on the target value. For example, X’s significance will be more on A, if even a small change in X can affect in changing the value of A. The F ratios are calculated by the Mean sum of squares of an entity and the mean sum of residuals squares. The mean sum of squares is calculated by dividing the mean sum of squares by the degree of freedom. The degree of freedom is the number of possible cases of the nominal variable, minus one.

F critical is based on the significance values. F ratios are calculated manually through the process explained above. The validity of the hypothesis is dependent on the values of F ratios and F critical. Here are the cases:

· If the F-critical > F ratio, then the hypothesis holds, and there is no relation between the variables under observation

· If the F-critical < F ratio, then the hypothesis can be declared invalid, and in turn, supports the idea that the variables affect each other.

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Difference between One-way and two-way

As mentioned, here, we discuss the concept of Anova two-factor with replication. But what exactly is the difference between one-factor and two-factor? Anova one-factor deals with only one nominal variable (A variable that has two or more classes or categories, but the order of categories is not crucial. For example, gender is a nominal variable with classes male and female).

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However, Anova two-factor deals with two nominal variables. As the variables are fewer, there is also a change in the number of the null hypothesis in both the types of analysis. The hypotheses in two-way Anova are as follows:

· The means of observation by one variable is the same. Meaning, variable one does not affect the target value in any way.

· The means of observation by the other variable is the same. Meaning, variable two does not affect the target value in any way.

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· There is no interaction between the variable one and variable two.

In one-way Anova, there is a null hypothesis and an alternative hypothesis. First, the means by the variable is the same, and second, the means by the other variable is the same.

To understand more clearly, let us take the help of an example.

Example #1

SIDHigh NoiseSIDMedium NoiseSIDLow Noise

The table shows the marks of different students in the presence of a different range of noises. In a one-way anova, only one nominal variable is there. Here, the nominal variable is noise. So, the hypothesis will try to check if noise has a significant effect on the marks of students or not.

Let us take another table:

StudentHigh NoiseMedium NoiseLow Noise

Now in this table, the marks are shown with categories of students. Hence, we have two nominal variables, the gender of the student and the noise level. Here, there can be two-factor analysis, which will be done using three hypotheses.

But now what exactly is meant by Anova two-factor with replication?

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Difference between with-replication and without-replication

The fundamental difference between Anova two-factor with replication and without replication is that the sample size is different. In the technique with-replication, the total number of samples is mostly uniform. If that is the case, the means are calculated independently. This type of data is also known as balanced data. But if the sample size is not uniform, the analysis is difficult. It is better to get the sample size uniform to get faster results.

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In the technique without replication, the sample observation size is one. It means that there is only a single observation for each combination of nominal variables. Here, the analysis can be done using the means of both the variables as well as the total mean of considering every observation as a single cluster. The F-ratio can then be calculated by the remainder mean and the total mean.

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So, this is how Anova two-factor with replication works. There are many such concepts in statistics where the calculation seems difficult, but things get simpler if there is conceptual clarity. We discussed what is meant by Anova, the concept, two-way Anova, and the replication criteria. We hope the article has provided enough details on Anova two-factor workings with replication for you to try out on your own.  

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Rohit Sharma

Blog Author
Rohit Sharma is the Program Director for the UpGrad-IIIT Bangalore, PG Diploma Data Analytics Program.

Frequently Asked Questions (FAQs)

1Is the t-test the same as the Anova?

The t-test examines if two populations are statistically distinct, whereas the Anova tests whether three or more populations are statistically dissimilar. For comparing the means of two groups, the t-test is employed, but the Anova is used when comparing the means of three or more groups. In Anova, the first step is to find a common P value. A significant P value in the Anova test indicates that the mean difference between at least one pair was statistically significant.

2In Anova, how do you accept or reject the null hypothesis?

The typical interpretation is that the data is statistically significant when the p-value is less than the significance level, and you reject H 0. When there is enough information to identify that not all of the means are equal, we may reject the null hypothesis in one-way Anova.

3In Anova, how do you interpret the F value?

The significance of F is the probability that the null hypothesis of your regression model cannot be rejected. To put it another way, it indicates the probability that all of the coefficients in your regression result are zero! The difference between two mean square values is equivalent to the F ratio. If the null hypothesis is accurate, F should be close to 1.0 the vast majority of the time. A high F ratio implies that group mean variance is higher than would be anticipated by chance.

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