Hypothesistesting2

For dummies !!

A hypothesis is a prediction about the outcome of an experiment. In market research this could be the result of the out come of a focus or field study

Hypothesis testing is a procedure through which sample data is used to evaluate the credibility of a hypothesis

State a hypothesis
Usually in terms of the value of a experiment parameter.
If the data are consistent with the hypothesis, conclude that the hypothesis was reasonable, and fail to reject it

Shoppers in a store playing music shop spend more.
Independent Variable:
Music in the store
Dependent Variable:
Amount spent in store

Obtain a random sample of shoppers who go to stores with music
Check shop spending
Compare sample data to hypothesis
Make decision:
Reject the hypothesis
Fail to reject the hypothesis

The effect of the Independent Variable (treatment effect) is assumed to:
Add (or subtract) a constant from every individual’s score

Can’t prove hypothesis
Proof requires evidence for all cases

Determine the number of samples (groups, conditions)
One
Two
k (three or more)

If there are two or more samples, determine whether they are independent or dependent
Same group (repeated-measures)
Match on some other variable(s) known to influence DV (matched-subjects)

If there is one sample and the Dependent Variable is at the Interval or Ratio Level of Measurement, is the standard deviation of the population (  , sigma) known:
If  is known, use a One-Sample z-Test
If  is unknown, use a One-Sample t-Test

Identify the independent variable
Identify the dependent variable and its level of measurement
Identify the population to which inferences will be made

Determine the appropriate inferential statistical test
Number of samples
Nature of samples (if applicable)
Level of measurement of DV
State the null hypothesis
State the alternative hypothesis

State Decision Rule:
If the p-value of the obtained test statistic is less than .05, reject the Null Hypothesis
Use SPSS to compute the obtained test statistic
Make decision
Interpret results

State the hypotheses

State the null hypothesis

The null hypothesis predicts that the Independent Variable (treatment) will have no effect on the Dependent Variable for the population

The alternative hypothesis predicts that the Independent Variable (treatment) will have an effect on the Dependent Variable for the population

Researcher has reason to believe before conducting the test that a difference will lie in a specified direction
Prior research
Theory

Researcher has no reason to believe that there will be a difference in a specified direction

Because of sampling error, there is likely to be a discrepancy between the sample mean and the population mean

Obtained test statistic

Reject the null hypothesis
If sample data is unlikely to have been drawn from a population where the null hypothesis is true
If the p-value of the obtained test statistic is less than .05

Either:
Treatment had an effect, could not demonstrate it
or
Treatment had no effect

Actual State of Affairs Belief Decision H 0 is True H 0 is False H 0 is False Reject H 0 Type I Error False Positive  Correct Rejection 1 -  Power H 0 is True Fail to Reject H 0 Correct Failure to Reject 1 -  Type II Error False Negative 

Committed when H 0 is rejected as false although it is true

Committed when H 0 is not rejected although it is false

Probability that the test will correctly reject a false null hypothesis

When a treatment effect exists
A study may fail to discover it (Type II error, fail to reject a false null hypothesis)
A study may discover it (reject a false null hypothesis)

Reducing alpha (.05 --> .01 --> .001)
Reduces power
Inverse relationship between Type I and Type II errors

Some inferential statistical tests are more powerful

Did Not Commit Crime Committed Crime Guilty Type I Error Convict Innocent Person Correct Verdict Convict Guilty Person Not Guilty Correct Acquittal Fail to Convict Innocent Person Type II Error Fail to Convict Guilty Person

Alpha: probability of committing a Type I error
Reject H 0 although it is true
Symbolized by 

Obtained result attributed to:
Real effect (reject H 0 )
Chance

Hypothesistesting2

by nithinr_2001

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