# When to use t test vs z test

## When should we use t test than Z test?

Z-Test or T-test, what test should I use? When you know the population standard deviation you should use the Z-test,

**when you estimate the sample standard deviation**you should use the T-test. Usually, we don’t have the population standard deviation, so we use the T-test.## Why do we use t test instead of Z test?

Z Test is the statistical hypothesis which is used in order to determine that whether the two samples means calculated are different in case the standard deviation is available and sample is large whereas the T test is used

**in order to determine a how averages of different data sets differs from each other in case**…## What is the difference between z test and t test?

**Z-tests are statistical calculations that can be used to compare population means to a sample’s.**

**T-tests are calculations used to test a hypothesis**, but they are most useful when we need to determine if there is a statistically significant difference between two independent sample groups.

## When should you use the t test?

When to use a t-test

A t-test can only be used **when comparing the means of two groups** (a.k.a. pairwise comparison). If you want to compare more than two groups, or if you want to do multiple pairwise comparisons, use an ANOVA test or a post-hoc test.

## Is t-test used for categorical variables?

**They can be used to test the effect of a categorical variable on the mean value of some other characteristic**. T-tests are used when comparing the means of precisely two groups (e.g. the average heights of men and women).

## What is the difference between Z and T distributions?

What’s the key difference between the t- and z-distributions?

**The standard normal or z-distribution assumes that you know the population standard deviation.****The t-distribution is based on the sample standard deviation**.## What is Z-test used for?

A z-test is a statistical test used

**to determine whether two population means are different when the variances are known and the sample size is large**.## Which hypothesis test should I use?

The test we need to use is a

**one sample t-test for means**(Hypothesis test for means is a t-test because we don’t know the population standard deviation, so we have to estimate it with the sample standard deviation s).## What is the main difference between z-score and T score?

The main difference between a z-score and t-test is that the z-score assumes you do/don’t know the actual value for the population standard deviation, whereas the t-test assumes you do/don’t know the actual value for the population standard deviation.

## What is the t-distribution used for?

The t-distribution is used

**when data are approximately normally distributed**, which means the data follow a bell shape but the population variance is unknown. The variance in a t-distribution is estimated based on the degrees of freedom of the data set (total number of observations minus 1).## Why do we use the t-distribution instead of the normal distribution?

The t-distribution is used as an alternative to the normal distribution

**when sample sizes are small in order to estimate confidence or determine critical values that an observation is a given distance from the mean**.## Should I use T-score or z-score?

You must know the standard deviation of the population and your sample size should be above 30 in order for you to be able to use the z-score. Otherwise,

**use the t-score**.## Which of the following is a difference between Z tables and T tables?

Normally, you use the t-table when the sample size is small (n<30) and the population standard deviation Ïƒ is unknown. Z-scores are based on your knowledge about the population’s standard deviation and mean.

**T-scores are used when the conversion is made without knowledge of the population standard deviation and mean**.## Which of the following is a fundamental difference between the T and Z statistic?

The correct answer is b)

**the t statistic uses the sample variance in place of the population variance**.## What is an advantage of T scores over z scores?

For example, a t score is a type of standard score that is computed by multiplying the z score by 10 and adding 50. One advantage of this type of score is that

**you rarely have a negative t score**. As with z scores, t scores allow you to compare standard scores from different distributions.## What is the difference between T-score and z-score in osteoporosis?

DEXA scores are reported as “T-scores” and “Z-scores.” The T-score is a comparison of a person’s bone density with that of a healthy 30-year-old of the same sex. The Z-score is a comparison of a person’s bone density with that of an average person of the same age and sex.

## Why are t statistics more variable than z scores quizlet?

why are t statistics more variable than z scores?

**The t statistic uses the sample variance in place of the population variance**.## What is an advantage of T scores over z-scores quizlet?

What is an advantage of T scores over z scores?

**The mode is not often used**.## What do T scores mean in osteoporosis?

**A T-score between âˆ’1 and âˆ’2.5 indicates that you have low bone mass, although not low enough to be diagnosed with osteoporosis**. A T-score of âˆ’2.5 or lower indicates that you have osteoporosis. The greater the negative number, the more severe the osteoporosis.

## What is a normal T and Z-score for bone density?

**A T-score of -1.0 or above**is normal bone density. Examples are 0.9, 0 and -0.9. A T-score between -1.0 and -2.5 means you have low bone mass or osteopenia. Examples are T-scores of -1.1, -1.6 and -2.4.

## What is BMD test?

A bone mineral density (BMD) test

**measures how much calcium and other types of minerals are in an area of your bone**. This test helps your health care provider detect osteoporosis and predict your risk for bone fractures.## What is the lowest T-score for osteoporosis?

A T-score within 1 SD (+1 or -1) of the young adult mean indicates normal bone density. A T-score of 1 to 2.5 SD below the young adult mean (-1 to -2.5 SD) indicates low bone mass. A T-score of

**2.5 SD or more below the young adult mean (more than -2.5 SD)**indicates the presence of osteoporosis.