Lecture 4.2 Sample estimation Flashcards

1
Q

why do we draw a sample from a population?

A

cheaper and easier than measuring the entire population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what does a sampling strategy depend on?

A

the sample being representative of the population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is a population?

A

group of individuals where we wish to measure a variable of interest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is a population parameter?

A

summary values from populations e.g means ect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is a sample?

A

subset of a population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

whats an underlying assumption from a sample?

A

sample is drawn at random

values in the sample are independent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what does accuracy mean?

A

Free from bias

  • sample means should be measured from the same samples within the same population
  • results would ideally be centered around the true population mean
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does precision mean?

A

Repeat-ability

-sample means calculated from repeated samples of the same population and should show little variation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When is accuracy affected?

A

when we are affected in our ability to select a truly representative sample

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

when is precision affected?

A

depends on sample size and population variance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

when is a statistic used to estimate a parameter unbiased?

A

mean of the sampling distribution is equal to the true value of the parameter being measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the variability of a statistic ?

A

spread of its sampling distribution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is a high bias?

A

spread away from the true value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is high variability?

A

the data not being close together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how can you reduce variability and bias?

A

random sample

large sample size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the sample distribution?

A

frequency distribution of a statistic over an infinite samples of a given size from a population

17
Q

what does the sample distribution represent?

A

how far the sample mean is from the population mean for any randomly selected sample

18
Q

what does the sample distribution show as the sample size increases?

A

sample distribution of the mean should show a normal distribution

19
Q

what is the standard error?

A

standard deviation of the sampling distribution

20
Q

what does the standard error measure?

A

measures precision in terms of how much any sample statistic varies from one sample to another

21
Q

why cant we usually determine the sampling distribution of the mean?

A

population is not known

22
Q

what do we do as we cannot determine the sampling distribution?

A

Sample mean would estimate the unknown population mean

Sample standard deviation would estimate the standard error.

23
Q

how is standard error calculated?

A

sample standard deviation dividied by the square root of the sample size

24
Q

when will the mean of the sample distribution take the form of normal distribution?

A

large sample size n>30

irrespective of the distribution of the variable in the population

25
what does central limit theorem allow?
allows the sampling distribution of a statistic to be approximated from a sample
26
what two things affect the range of the confidence interval?
variation --> less variation means a smaller confidence interval sample size --> larger sample size means a smaller confidence interval
27
what does a 95% confidence interval mean?
95% of repeated samples from this population will produce a plausible range of values which include the population parameter
28
what happens when the sample size is less than 30
central limit theorem is no longer valid
29
what is the student t-test and when do you use it?
when <30 samples t-test applied with n-1 degrees of freedom (number of observations -1) VARIABLE OF INTEREST MUST BE NORMALLY DISTRIBUTED IN THE POPULATION