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# Hypothesis Testing - PowerPoint PPT Presentation

Hypothesis Testing. Central Limit Theorem. Hypotheses and statistics are dependent upon this theorem. Central Limit Theorem. To understand the Central Limit Theorem we must understand the difference between three types of distributions….

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### Hypothesis Testing

Hypotheses and statistics are

dependent upon this theorem

To understand the Central Limit Theorem

we must understand the difference between

three types of distributions…..

A distribution is a type of graph showing the frequency

of outcomes:

Of particular interest is the “normal distribution”

distributions, even for the same variable…

• Population distributions

• Population distributions

• Population distributions

• Population distributions

• Population distributions

• Population distributions

• Sample distributions

• Population distributions

• Sample distributions

• Population distributions

• Sample distributions

• Samplingdistributions

The frequency distributions of samples.

The sample distribution should look like

the population distribution…..

Why?

The frequency distributions of samples.

3. Samplingdistributions

The frequency distributions of statistics.

The frequency distributions of samples.

The sampling distribution should NOT look like

the population distribution…..

Why?

looked like these:

a random sample from this population of a certain

size n… over and over again and calculated the

mean each time……

those means. This would be a sampling

distribution of means.

of the sample means would be larger than 40,

and how many would be less than 40?

below, the sampling distribution would be

symmetrical around the population mean of 40.

together (have less variance) if the variance of

the population is smaller.

together (have less variance) if the size of

each sample (n) gets larger.

Sample

So the sampling distribution will have a mean

equal to the population mean, and a variance

inversely proportional to the size of the sample (n),

and proportional to the variance of the population.

If samples are large, then

the sampling distribution created by those

samples will have a meanequal to the

population mean and a standard deviation

equal to the standard error.

because all the characteristics of a normal curve

are known.

http://www.statisticalengineering.com/central_limit_theorem.htmhttp://www.statisticalengineering.com/central_limit_theorem.htm

A great example of the theorem in action….

Another great example of the theorem in action….

A statistic tests a hypothesis: H0

A statistic tests a hypothesis: H0

The alternative or default hypothesis is: HA

A statistic tests a hypothesis: H0

The alternative or default hypothesis is: HA

A probability is established to test the

“null” hypothesis.

95% confidence: would mean that there

would need to be 5% or less probability of

getting the null hypothesis; the null

hypothesis would then be dropped in

favor of the “alternative” hypothesis.

95% confidence: would mean that there

would need to be 5% or less probability of

getting the null hypothesis; the null

hypothesis would then be dropped in

favor of the “alternative” hypothesis.

1 - confidence level (.95) = alpha

Type I Error: saying nothing is

happening when something is:

p = alpha

Type I Error: saying something is

happening when nothing is:

p = alpha

Type II Error: saying nothing is

happening when something is:

p = beta

An example from court cases:

http://www.intuitor.com/statistics/T1T2Errors.html

Care must be taken when using hypothesis testing…https://www.khanacademy.org/math/probability/statistics-inferential/sampling_distribution/v/sampling-distribution-example-problem

PROBLEMS

I hypothesize that a barking dog is hungry.

The dog barks, is the dog therefore hungry?https://www.khanacademy.org/math/probability/statistics-inferential/sampling_distribution/v/sampling-distribution-example-problem

prior information.

For example, how often does the dog bark when it is not hungry.

a hundred times….

It came up heads 60 times.

Is it a fair coin?

Because of the Z-test finds that the probability of doing

that is equal to 0.0228.

We would reject the Null Hypothesis!

coin a hundred times again…

It came up tails 60 times.

Is it a fair coin?

But we have now thrown thehttps://www.khanacademy.org/math/probability/statistics-inferential/sampling_distribution/v/sampling-distribution-example-problem

coin two hundred times, and…

It came up tails 100 times.

Is it a fair coin?

The probability of rejecting the null hypothesis is now ZERO!!

Poggendorf figure to one side

of the brain or to the other….

and measure error.

Mean N Std. Error Mean

Pair 1 Right 5.4167 12 .70128

Left 4.9167 12 .62107

t(11) = 2.17, p = 0.053

What do you conclude?

Mean N Std. Error Mean

Pair 1 Right 5.4167 12 .70128

Left 4.9167 12 .62107

t(11) = 2.17, p = 0.053

Now suppose you did this again

with another sample of 12 people.

t(11) = 2.10, p = 0.057

But the probability of independent events is:https://www.khanacademy.org/math/probability/statistics-inferential/sampling_distribution/v/sampling-distribution-example-problem

p(A) X p(B) so that:

The Null hypothesis probability for both studies was:

0.053 X 0.057 = 0.003

What do you conclude now?

hemispheres are truly

independent….

Then...

Mean N Std. Error Mean

Pair 1 Right 5.4167 12 .70128

Left 4.9167 12 .62107

t(22) = 0.53, p = 0.60

What do you conclude now?