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Performing a t-test in Python | Statistical Testing
Learning Statistics with Python
course content

Course Content

Learning Statistics with Python

Learning Statistics with Python

1. Basic Concepts
2. Mean, Median and Mode with Python
3. Variance and Standard Deviation
4. Covariance vs Correlation
5. Confidence Interval
6. Statistical Testing

bookPerforming a t-test in Python

To conduct a t-test in Python, all you have to do is specify the alternative hypothesis and indicate whether variances are roughly equal (homogeneous).

The ttest_ind() function within scipy.stats handles the rest. Below is the syntax:

Parameters:

  • a — the first sample;
  • b — the second sample;
  • equal_var — set to True if variances are approximately equal, and False if they are not;
  • alternative — the type of alternative hypothesis:
    • 'two-sided' — indicates that the means are not equal;
    • 'less' — implies that the first mean is less than the second;
    • 'greater' — implies that the first mean is greater than the second.

Return values:

  • statistic — the value of the t statistic;
  • pvalue — the p-value.

We are interested in the pvalue. If it is lower than α(usually 0.05), then the t statistic is in the critical region, so we should accept the alternative hypothesis. And if pvalue is greater than α — we accept the null hypothesis that means are equal.

Here is an example of applying the t-test to our heights dataset:

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import pandas as pd import scipy.stats as st # Load the data male = pd.read_csv('https://codefinity-content-media.s3.eu-west-1.amazonaws.com/a849660e-ddfa-4033-80a6-94a1b7772e23/Testing2.0/male.csv').squeeze() female = pd.read_csv('https://codefinity-content-media.s3.eu-west-1.amazonaws.com/a849660e-ddfa-4033-80a6-94a1b7772e23/Testing2.0/female.csv').squeeze() # Apply t-test t_stat, pvalue = st.ttest_ind(male, female, equal_var=True, alternative="greater") if pvalue > 0.05: # Check if we should support or not the null hypothesis if pvalue > 0.05: print("We support the null hypothesis, the mean values are equal") else: print("We reject the null hypothesis, males are taller")
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Section 6. Chapter 6
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