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# Testofhypothesis

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### Transcript of "Testofhypothesis"

1. 1. IntroductionHypothesis is usually considered as the principal instrument in research.Its main function is to suggest new experiments and observations.In fact, many experiments are carried out with the deliberate object of testing hypotheses.Decision-makers often face situations where in they are interested in testing hypotheses on the basis of available information and then take decisions on the basis of such testing.
2. 2. • Ordinarily, when one talks about hypothesis, one simply means a mere assumption or some supposition to be proved or disproved.• But for a researcher hypothesis is a formal question that he intends to resolve.• Thus a hypothesis may be defined as a proposition or a set of proposition set forth as an explanation for the occurrence of some specified group of phenomena either asserted merely as a provisional conjecture to guide some investigation or accepted as highly probable in the light of established facts.• Quite often a research hypothesis is a predictive statement, capable of being tested by scientific methods, that relates an independent variable to some dependent variable. What Is A Hypothesis?
3. 3. WHAT IS A HYPOTHESIS...ExampleThe mileage of automobile A is as good as automobile bThe customer loyalty of brand A is better than brand B.These hypotheses are capable of objectively verified and tested
4. 4. STEPS IN HYPOTHESIS TESTING PROCEDURE EVALUATE DATA REVIEW ASSUMPTIONS STATE HYPOTHESIS SELECT TEST STATISTICS DETERMINE DISTRIBUTION OF TEST STATISTICS State decision rule CALCULATE TEST STATISTICS Do not MAKE STATISTICAL Reject Reject H0 DECISION H0Conclude H0 Conclude H1May be true Is true
5. 5. Characteristics of a hypothesis Conceptual Clarity -Hypothesis should be clear - and precise. Testability -Hypothesis should be capable of - being tested. Consistency - It should be consistent with the objectives of research. Expectancy -Hypothesis should be able to state - relationship between variables, if it happens to be a relational hypothesis.
6. 6.  Specificity -Hypothesis should be limited in - scope and must be specific. Narrower hypothesis are easily testable. Simplicity -Hypothesis should be stated as far - as possible in most simple terms so that the same is easily understandable by all concerned. Theoretical Relevance -Hypothesis should be - consistent with most known facts i.e., it must be consistent with a substantial body of established facts.
7. 7. Objectivity - It should not include value judgments, relative terms or any moral preaching.Availability of Techniques – Statistical methods should be available for testing the proposed hypothesis.Hypothesis should be amenable to testing within a reasonable timeHypothesis must explain the facts that give rise to the need for explanation
8. 8. Parametric and Standard Test BASIC CONCEPTS CONCERNING TESTING OF HYPOTHESES Null hypothesis and alternative hypothesis The level of significance Decision rule or test of hypothesis Type I and Type II Errors Two-tailed and One-tailed tests
9. 9. Basic concepts concerning testing of hypothesisNull Hypothesis and alternative hypothesis• In statistical analysis if we want to compare method A with method B and if we proceed with the assumption that both methods are equally good then this assumption is termed as null hypothesis.
10. 10. Basic concepts concerning testing of hypothesis• As against this we may feel that method A is better than method B then we call it as alternative hypothesis• Null Hypothesis is generally is termed as H0• Alternative hypothesis symbolized as Ha
11. 11. Basic concepts concerning testing of hypothesis• Suppose we want to test the hypothesis that the population mean (µ) is equivalent to hypothesised mean then (µH0 )= 100• Then null hypothesis would be population mean is equal to hypothesised mean• Ho: µ= µHo = 100
12. 12. Three Possible alternative hypothesesAlternative hypothesis To be read as followsHa : µ ≠µH0 The alternative hypothesis is that the population mean is not equal to 100 i.e., it may be more or less than 100Ha : µ > µH The alternative hypothesis is that the 0 population mean is greater than 100Ha : µ < µH0 The alternative hypothesis is that the population mean is less than 100
13. 13. Possible Rejection and Nonrejection Regions Rejection region for hypothesis which involve the standard normal distribution and the ≠ symbol (two –tailed test)
14. 14. Possible Rejection and Nonrejection Regions Rejection region for hypothesis which involve the standard normal distribution and the > symbol (right –tailed test)
15. 15. Possible Rejection and Nonrejection Regions Rejection region for hypothesis which involve the standard normal distribution and the < symbol (left –tailed test)
16. 16. In the choice of null hypothesis, the followingconsiderations are usually kept in view: • Alternative hypothesis is usually the one which one wishes to prove and the null hypothesis is the one which one wishes to disprove. • Thus, a null hypothesis represents the hypothesis we are trying to reject, and alternative hypothesis represents all other possibilities
17. 17. In the choice of null hypothesis, the following considerations are usually kept in view:• If the rejection of a certain hypothesis when it is actually true involves great risk, it is taken as null hypothesis because then the probability of rejecting it when it is true is α (the level of significance) which is chosen very small.• Null hypothesis should always be specific hypothesis i.e., it should not state about or approximately a certain value.
18. 18. The level of significance• This is a very important concept in the context of hypothesis testing.• It is always some percentage (usually 5%) which should be chosen wit great care, thought an reason. In case we take the significance level at 5 per cent, then this implies that H0 will be rejected• If a hypothesis is of the type µ =µH0, then we call such a hypothesis as simple (or specific) hypothesis but if it is of the type µ ≠ µH0 or µ> µH0 or µ<µH0 then we call it a composite (or nonspecific) hypothesis.
19. 19. Decision rule or test of hypothesis• Given a hypothesis H0 and an alternative hypothesis Ha, we make a rule which is known as decision rule according to which we accept H0 (i.e., reject Ha) or reject H0 (i.e., accept Ha).• For instance, if (H0 is that a certain lot is good (there are very few defective items in it) against Ha) that the lot is not good (there are too many defective items in it), then we must decide the number of items to be tested and the criterion for accepting or rejecting the hypothesis.• We might test 10 items in the lot and plan our decision saying that if there are none or only1 defective item among the 10, we will accept H0 otherwise we will reject H0 (or accept Ha). This sort of basis is known as decision rule.
20. 20. Type I and Type II errorsWe may reject H0when H0is true and we may accept H0when in fact H0 is not true. The former is known as Type I error and the latter as Type II error.• Type I Error – Rejecting a true null hypothesis – Type I error means rejection of hypothesis which should have been accepted – The probability of committing a Type I error is called α, the level of significance.• Type II Error – Failing to reject a false null hypothesis – Type II error means accepting the hypothesis which should have been rejected. – The probability of committing a Type II error is called β.
21. 21. Type I and Type II Errors State of World Decision Ho true H1 true (Ho false) Cannot reject Correct Type II error (“accept”) Ho decision Reject Ho Type I error Correct decision Need to control both types of error: α = P(rejecting Ho|Ho) β = P(not rejecting Ho|H1)
22. 22. Type I and Type II Errors• Definition: Type I and Type II errorsA Type I error is the error of rejecting H0 when it is true. A Type IIerror is the error of accepting H0 when it is false (that is when H1 istrue).• Notation: Probability of Type I error: a = P[X ∈ R|H0] Probability of Type II error: b = P[X ∈ RC|H1]• Definition: Power of the testThe probability of rejecting H0 based on a test procedure is called thepower of the test. It is a function of the value of the parameters tested,θ: π = π(θ) = P[X ∈ R]. Note: when θ ∈ H1 => π(θ) = 1- b(θ).
23. 23. Type I and Type II Errors• We want π(θ) to be near 0 for θ ∈ H0, and π(θ) to be near 1 for θ∈ H1.• Definition: Level of significanceWhen θ ∈ H0 α, π(θ) gives you the probability of Type I error. Thisprobability depends on θ. The maximum value of this when θ ∈ H0is called level of significance (significance level) of a test, denotedby α. Thus, α = supθ ∈ H0 P[X ∈ R|H0] = supθ ∈ H0 π(θ)Define a level α test to be a test with supθ ∈ H0 π(θ) ≤ α.Sometimes, α. is called the size of a test.
24. 24. Type I and Type II Errors 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 H0 H1 β = Type II error α = Type I error π = Power of test
25. 25. TWO TAILED AND ONE TAILED TEST• A two tailed test reject the null hypothesis if, say the sample mean is significantly higher or lower than the hypothesised value of mean population.• Symbolically, the two tailed test is appropriate when we have H₀:μ=μH₀ and Ha: μ≠ μH₀ which may mean μ>μH₀ or μ<μH₀.• Thus, in a two tailed test, there are two rejection regions.
26. 26. A one tailed test is used when we have to test whether populationmean is either lower than or higher than some hypothesisedvalue.In this if the rejection region on the left it is called left tailedtest .It is represented as-H₀: μ= μH₀ and Ha: μ< μH₀ If the rejection is on the right side it is called right tailed test.It is denoted byH₀: μ= μH₀ and Ha: μ> μH₀
27. 27. One-tail vs. Two-tail Test
28. 28. One-Tailed Test versus Two-Tailed Test
29. 29. PROCEDURE FOR HYPOTHESIS TESTING• Procedure for hypothesis testing refers to all those steps that we undertake for making a choice between the two actions i.e., rejection and acceptance of a null hypothesis. The various steps involved in hypothesis testing are stated below: Making a formal statement Selecting a significance level Deciding the distribution to use Selecting a random sample and computing an appropriate value Calculation of the probability Comparing the probability
30. 30. Making a formal statement• The step consists in making a formal statement of the null hypothesis (H0) and also of the alternative hypothesis (Ha). This means that hypotheses should be clearly stated, considering the nature of the research problem.• For instance, Mr. Mohan of the Civil Engineering Department wants to test the load bearing capacity of an old bridge which must be more than 10 tons, in that case he can state his hypotheses as under: – Null hypothesis H0 : µ = 10 tons – Alternative Hypothesis Ha: µ > 10 tons
31. 31. Making a formal statement…• Take another example. The average score in an aptitude test administered at the national level is 80.• To evaluate a state’s education system, the average score of 100 of the state’s students selected on random basis was 75. The state wants to know if there is a significant difference between the local scores and the national scores. In such a situation the hypotheses may be stated as under: • Null hypothesis H0: µ = 80 • Alternative HypothesisHa: µ ≠ 80
32. 32. Making a formal statement…• The formulation of hypotheses is an important step which must be accomplished with due care in accordance with the object and nature of the problem under consideration.• It also indicates whether we should use a one-tailed test or a two-tailed test. If Ha is of the type greater than (or of the type lesser than), we use a one-tailed test, but when Ha is of the type “whether greater or smaller” then we use a two-tailed test.
33. 33. Selecting a significance level• The hypotheses are tested on a pre-determined level of significance and as such the same should be specified. Generally, in practice, either 5% level or 1% level is adopted for the purpose. The factors that affect the level of significance are:  the magnitude of the difference between sample means;  the size of the samples;  the variability of measurements within samples;  whether the hypothesis is directional or non-directional (A directional hypothesis is one which predicts the direction of the difference between, say, means).• The level of significance must be adequate in the context of the purpose and nature of enquiry.
34. 34. Deciding the distribution to use• Hypothesis testing is to determine the appropriate sampling distribution.• The choice generally remains between normal distribution and the t-distribution.• The rules for selecting the correct distribution are similar to those which we have stated earlier in the context of estimation.
35. 35. Selecting a random sample and computing an appropriate value• Select a random sample(s) and compute an appropriate value from the sample data concerning the test statistic utilizing the relevant distribution.• In other words, draw a sample to furnish empirical data.
36. 36. Calculation of the probability• One has then to calculate the probability that the sample result would diverge as widely as it has from expectations, if the null hypothesis were in fact true.
37. 37. Comparing the probability• Comparing the probability thus calculated with the specified value for α the significance level.• If the calculated probability is equal to or smaller than the α value in case of one-tailed test (and α/2 in case of two-tailed test), then reject the null hypothesis (i.e., accept the alternative hypothesis), but if the calculated probability is greater, then accept the null hypothesis.• In case we reject Ho we run a risk of (at most the level of significance),committing an error of Type I, but if we accept H0, then we run some risk (the size of which cannot be specified as long as the H0 happens to be vague rather than specific) of committing an error of Type II.•
38. 38. conclusion• From this I conclude that “ an effective research can’t be fulfill the objectives without Hypothesis”• So a researcher should have a thorough knowledge in this field of fixing and testing of hypothesis.