How to determine whether to conduct a two tailed or one tailed hypothesis test

When carrying out hypothesis tests, it is important to know what type of hypothesis test to perform because there are three types of tests in particular to choose from, being

1. Two tail test
2. One tailed test on the left side
3. One tailed test on the right side

Four steps involved in conduction a hypothesis test are:-

1. Formulate the null and alternate hypothesis
2. Calculate the t-statistic
3. Calculate the cutoff values for the t-statistic
4. Check whether the t-statistic falls within the rejection region

Two tailed test

A two tailed test is performed if you want to determine if there is difference in direction, being an increase or decrease, from a specific value:-

• Null hypothesis H0 sample population mean = sample mean
• Alternate hypothesis Ha population mean <> sample mean

An example of a two tailed test in Python can be seen below:-

A battery has a lifespan of 300 hours. Take a random sample of 30 batteries to measure their lifespans to see if they deviate from the expected lifespan of 300 hours.