Dr. Athar Khan Associate Professor Department of Community Medicine Liaquat College of Medicine & Dentistry matharm@yahoo.com

1. Hypothesis Testing & p-value
Dr. Athar Khan
MBBS, MCPS, DPH, MBA, DCPS-HPE, DCPS-HCSM,
PGD-Statistics, BA, MA, PhD Scholar
Associate Professor
Department of Community Medicine
Liaquat College of Medicine & Dentistry
matharm@yahoo.com

2. CHAPTER # of BCQ’s #EMQ’s
General epidemiology and screening 9 1
Demography and population dynamics 7 1
Biostatistics 5 1
TOTAL MARKS 21 3

3. HYPOTHESIS
• Any statement about a population is termed as
hypothesis. OR
• A hypothesis is an educated guess or proposition
that attempts to explain a set of facts or natural
phenomenon. OR
• A hypothesis is a proposed explanation for a
phenomenon.

4. HYPOTHESIS
• Null Hypothesis(Ho) : There is NO difference or
association or relationship between the abdominal
and vaginal hysterectomy with respect to post
operative complications
• Alternate Hypothesis (Ha/H1) : There is a difference or
association or relationship between the abdominal
and vaginal hysterectomy with respect to post
operative complications

5. ALTERNATIVE HYPOTHESIS
• Alternative hypothesis is generally the research
question or researcher hypothesis.
• Null hypothesis is usually against the claim of the
researcher and every researcher would like to reject
this hypothesis

6. ALTERNATIVE HYPOTHESIS
• There is difference in complications between AH
and VH (Two Tailed/Two sided)
• VH has less complications than AH (One
Tailed/One sided)
• VH has more complications than AH (One
Tailed/One sided)

7. ALTERNATIVE HYPOTHESIS
• Our final decision is based on to:
– Reject the Null Hypothesis
– Fail to reject (accept) the Null Hypothesis

8. ONESIDEDorONETAILED
TWOSIDED
TWOTAILED
Rejection Area
Non-Rejection
Area

9. SITUATION ONE:
REJECT THE NULL HYPOTHESIS
TRUE SITUATION NULL HYPOTHESIS DECISION
REJECT Ho REJECTED RIGHT √
REJECT Ho NOT REJECTED WRONG

10. SITUATION TWO
FAIL TO REJECT THE NULL HYPOTHESIS
TRUE SITUATION NULL HYPOTHESIS DECISION
FAIL TO REJECT Ho NOT REJECTED RIGHT √
FAIL TO REJECT Ho REJECTED WRONG

11. • We make decision in research on the basis of
available evidence.
• Are we 100% sure?
• Is there a chance of error in our decision?
• Maximum 5% (0.05) is reasonable in making decision
about Ho. Sometimes 10% (0.1) and more accurate
1% (0.01) may be considered.

12. LEVEL OF SIGNIFICANCE OR Alpha 
• The chance of error which is set before starting
experiment and is fixed at 1%, 5%,10% is known as
level of significance of Alpha 
• 0.01 probability = 1%
• 0.05 probability = 5%
• 0.1 probability = 10%
MOST COMMON

13. CONFIDENCE LEVEL
Confidence Level = 1 – α
If α = 0.05
Confidence Level = 1 – α
Confidence Level = 1 – 0.05
Confidence Level = 0.95 or 95%
If α = 0.01 and α = 0.1
MOST COMMON

14. ONESIDEDorONETAILED
TWOSIDED
TWOTAILED
Significance Level
Confidence Level

15. TYPES OF ERRORS
DESIRE OF RESEARCHER IS TO REJECT Ho
TRUE SITUATION
DECISION Ho TRUE Ho FALSE
REJECT Ho Type I error or α error CORRECT
Fail to reject (accept) Ho CORRECT Type II error or β error
Type I error - α error (RTA):
Rejecting Ho when actually it is true.
Type II error - β error (AFB):
Fail to reject Ho when actually it is false.

16. What is Power of a Test?
– Power = P(reject null | null is false)
– It is the probability of rejecting Ho when Ho is indeed
false.
Power = 1 – β
If β = 20 then 1 – β = 80% so that we would have
rejected the false Ho about 80% of the time.

17. Hints for BCQ’s
– Alpha error s serious than Beta error
– Alpha error 5%(0.05) or less is acceptable
– Beta error 20%(0.20) or less is acceptable
– Power of the study 80%(0.80) or more is acceptable

18. P VALUE

19. DEFINITION
• Probability of committing Type I error OR
• Probability of rejecting Ho when actually it is true
OR
• Probability of falsely rejecting Ho OR
• Probability of getting a result by chance
• P-Values range from 0 to 1

20. P value and Significance level
• Level of significance is set before starting the
experiment and is fixed at 1%, 5%, 10% but P value
is calculated after completing the experiment and it
is not fixed.
• If p value is less than will reject Ho and if it is
more than  we will not reject Ho.

21. Interpreting p value
P value Inter pretation
P > 0.05 Result is not statistically significant
P < 0.05
Result is statistically significant *
<5% of committing Type I error
95% confident that real difference or not due to
chance
P < 0.01 Result is highly statistically significant **
P < 0.001
Result is very highly statistically significant ***
MOST COMMON