Sampling variability of a mean

5 important questions on Sampling variability of a mean

If we can assume our data is roughly normally distributed, what will be the summary statistics?

1. The mean (middle)
2. The standard deviation (spread)

What happens when the standard deviation changes?

The spread and height will change:
e.g. if the SD is smaller, the spread is reduced and the height of the distribution increases

Which inferences about the population from a single sample can we make due to theoretical relations about the sampling distribution?

1. The sampling distribution is normally distributed
      - If population distribution is approximately normal
      - If the sample size is large (regardless of population distribution)
2. The sampling distribution is centred around mu  (mean of the population)
3. The standard deviation (spread) of the sampling distribution is known as the standard error (SE)
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How do you interpret the 95% CI?

It expresses uncertainty of the sample mean as an estimate of the population mean due to sampling variation
Provides a plausible range of values for the true population mean (best estimate is the sample mean)
Will contain the true population mean 95% of the time on repeated sampling
From a single sample we can be 95% confident that the interval contains the true population mean.

What does the width of the CI depend on?

It depends on the standard error, which depends on the sample size and variability of the data

The question on the page originate from the summary of the following study material:

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