Students often go straight to the hypothesis test rather than first investigating the data with summary statistics and charts. Encourage them to summarise their data first. As well as summarising their results, graphs can show outliers and patterns.
For continuous, normally distributed data, summarise using means and standard deviations. If the data is skewed or there are influential outliers, the median (middle value) and interquartile range (Upper – lower quartile) are more appropriate.
T-tests are of different types:-
- Paired T-test – dependent and independent.
- Normal T-test
The paired t-test is used to determine paired differences. It is used in cases where the sample is less than 50, and the model on which the test was priory applied remains the same.
The One-sample t-test compares a sample mean to a specific value.
t = (mean – comparison value)/ Standard Error
An “F Test” uses the F-distribution. It uses an F Statistic to compare two variances.
i.e. s1 and s2, by dividing them. A result is always a number greater than zero (as variances are always positive). The equation for comparing two variances with the f-test is:
F = s21 / s22
It is also essential to understand the difference between a t-test and an f-test, as they are used interchangeably by many people.
Key Takeaways
- A t-test determines if two sets of data are significantly different.
- An F-test determines if two sets of data have the same variance.
- T-test is used for smaller sample sizes, while F-test is used for larger ones.
T-test vs F-test
Two data sets can be tested through a t-test. This test is done to check the difference between the given mean and sample mean. There can be different types of t-tests. F-test can be done to check the difference between two standard deviations. Standard deviations of two samples is compared in f-test.
Comparison Table
| Parameter of Comparison | T-test | F-test |
|---|---|---|
| Implication | The T-test is used to test the hypothesis of whether the given mean significantly different from the sample mean or not. | F-test is used to compare the two standard deviations of two samples and check the variability. An F-test is a ratio of two Chi-squares. |
| Types | T-tests are of different types:- 1. Paired T-test – dependent and independent. 2. Normal T-test | One type of F-test is used to compare the standard deviations of the two-sample data. |
| Null Hypothesis | H0: the sample mean is equal to 0. | H0: the two samples have the same variance. |
| Test statistic | T = (mean – comparison value)/ Standard Error ~t(n-1) | F = s21 / s22 ~ F(n1-1,n2-1) |
| Degree of freedom | The degree of freedom is )n-1) where n is the number of sample values | The degree of freedom is (n1-1,n2-1), where n1 and n2 are the numbers of observations in samples 1 and 2. |
What is T-test?
T distribution or t-test is used when the sample size,n, is less than 30 and the standard deviation, sigma, is unknown.
The normal distribution can closely approximate the distribution of continuous data.
T distribution is generally used to calculate numerical data.it is derived from a normal distribution and is also just a type of normal distribution.
One Sample t-test
The one-sample t-test is concerned with making inferences regarding a population mean.
One sample t-test is used when we are given only one sample, and we need to test a hypothesis on that sample.
Two Sample t-test
This is more common in a scenario than the one-sample t-test. Usually, we want to compare the means of 2 groups.
Two sample t-test is also used when we are given only one sample, and we need to run a hypothesis on that sample itself.
We can run two types of tests under this category.
- Paired test:- in this, the same sample population is used for testing two different treatments. Compare the means of two conditions in which the same (or closely matched) participants participated.
- Unrelated Samples:- In this, we compare the means of two groups of participants.
Hypothesis testing with t
- We can draw a sampling distribution of t-values (the Student t distribution) – this shows the likelihood of each t-value if the null hypothesis is true
- The distribution will be affected by sample size (or, more precisely, by degrees of freedom)
- We evaluate the likelihood of obtaining our t-value given the t-distribution.
Assumptions
The one-sample t-test requires the following statistical assumptions:
- Random and independent sampling.
- Data are from normally distributed populations.
[Note: The one-sample t-test is generally considered robust against violating this assumption once N > 30.]
What is F-test?
An “F Test” uses the F-distribution. It uses an F Statistic to compare two variances.
F-test for detecting the identity of variances of two normally distributed random variables:-
The so-called F-test checks our hypothesis for the identity of the variances of two independent random variables of a normal distribution with unknown expectations and variance.
H0: σ12 = σ22
H1: σ12 > σ22
The test is always carried out as a one-sided test.
Test statistics: Fsz = s12/s22 where s12 > s22
If H0 fulfils, then Fsz is of F-distribution with degrees of freedom n1-1, n2-1.
Decision principle: for Fsz ≤ Fα 0-hypothesis is accepted; otherwise, not.
Main Differences Between T-test and F-test
- The main difference between Reference and Recommendation is that a t-test is used to test the hypothesis of whether the given mean is significantly different from the sample mean or not. On the other hand, an F-test is used to compare the two standard deviations of two samples and check the variability.
- The T-test can be conducted as a two-sided or single-sided test, but the f-test is the only single-sided test as variance can not be negative.
- T-tests are of different types:- Paired T-test – dependent and independent, and Normal T-test. At the same time, the f-test is only of one kind.
- The T-test is applied when the sample population is less than 30, and the standard deviation is unknown, whereas the f-test can be devoted to a large sampled population.
- The T-test is used to check the hypothesis for the sample mean, whereas the f-test is used to run the hypothesis on the variance of the samples.
- https://asa.scitation.org/doi/abs/10.1121/1.417933
- https://projecteuclid.org/euclid.aoms/1177728261
- https://www.mitpressjournals.org/doi/abs/10.1162/089976699300016007
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Emma Smith holds an MA degree in English from Irvine Valley College. She has been a Journalist since 2002, writing articles on the English language, Sports, and Law. Read more about me on her bio page.
