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Statistics review 2: samples and populations.

Whitley E, Ball J - Crit Care (2002)

Bottom Line: The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset.However, a dataset is typically only of interest for the information it provides regarding the population from which it was drawn.The present review focuses on estimation of population values from a sample.

View Article: PubMed Central - PubMed

Affiliation: Lecturer in Medical Statistics, University of Bristol, UK. editorial@ccforum.com

ABSTRACT
The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset. However, a dataset is typically only of interest for the information it provides regarding the population from which it was drawn. The present review focuses on estimation of population values from a sample.

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The Normal and t (with 19 degrees of freedom) distributions.
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Figure 8: The Normal and t (with 19 degrees of freedom) distributions.

Mentions: The t-distribution is similar in shape to the Normal distribution, being symmetrical and unimodal, but is generally more spread out with longer tails. The exact shape depends on a quantity known as the 'degrees of freedom', which in this context is equal to the sample size minus 1. The t distribution for a sample size of 5 (degrees of freedom = 4) is shown in comparison to the Normal distribution in Fig. 7, in which the longer tails of the t-distribution are clearly shown. However, the t-distribution tends toward the Normal distribution (i.e. it becomes less spread out) as the degrees of freedom/sample size increase. Fig. 8 shows the t-distribution corresponding to a sample size of 20 (degrees of freedom = 19), and it can be seen that it is already very similar to the corresponding Normal curve.


Statistics review 2: samples and populations.

Whitley E, Ball J - Crit Care (2002)

The Normal and t (with 19 degrees of freedom) distributions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC137296&req=5

Figure 8: The Normal and t (with 19 degrees of freedom) distributions.
Mentions: The t-distribution is similar in shape to the Normal distribution, being symmetrical and unimodal, but is generally more spread out with longer tails. The exact shape depends on a quantity known as the 'degrees of freedom', which in this context is equal to the sample size minus 1. The t distribution for a sample size of 5 (degrees of freedom = 4) is shown in comparison to the Normal distribution in Fig. 7, in which the longer tails of the t-distribution are clearly shown. However, the t-distribution tends toward the Normal distribution (i.e. it becomes less spread out) as the degrees of freedom/sample size increase. Fig. 8 shows the t-distribution corresponding to a sample size of 20 (degrees of freedom = 19), and it can be seen that it is already very similar to the corresponding Normal curve.

Bottom Line: The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset.However, a dataset is typically only of interest for the information it provides regarding the population from which it was drawn.The present review focuses on estimation of population values from a sample.

View Article: PubMed Central - PubMed

Affiliation: Lecturer in Medical Statistics, University of Bristol, UK. editorial@ccforum.com

ABSTRACT
The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset. However, a dataset is typically only of interest for the information it provides regarding the population from which it was drawn. The present review focuses on estimation of population values from a sample.

Show MeSH