every research should know basic statistics : this is very important to perform sound methodology

1. Why to know statisticsWhy to know statistics

2.  To understand dataTo understand data

3. ExampleExample
 One of your colleague is an oncologyOne of your colleague is an oncology
surgeonsurgeon
 60% of his cases died60% of his cases died
 Does this mean that he is a looser!!Does this mean that he is a looser!!

4.  We should ask what are the resultsWe should ask what are the results
of his colleagues inof his colleagues in similarsimilar patientspatients
 How many patients he operatedHow many patients he operated
upon e.g 2/3!!!!upon e.g 2/3!!!!

5.  To summarize dataTo summarize data

6. ExampleExample
 Diastolic Blood pressureDiastolic Blood pressure
 80,70,65,90,74,80,60,90,60,75,80,980,70,65,90,74,80,60,90,60,75,80,9
0,100,100,100,950,100,100,100,95
 AgeAge
 24,30,26,40,28,21,26,31,32,36,27,424,30,26,40,28,21,26,31,32,36,27,4
5,62,58,52,50,605,62,58,52,50,60

7. Vital for researchVital for research
 Without the use of statistics it wouldWithout the use of statistics it would
be very difficult to make decisionsbe very difficult to make decisions
based on the data collected from abased on the data collected from a
research projectresearch project

8. Statistical steps in researchStatistical steps in research
 Collect dataCollect data
 Organise dataOrganise data
 Analyse dataAnalyse data
 Interpret the dataInterpret the data
 Present the dataPresent the data

9. How to read the resultsHow to read the results
 An understanding of basic statisticsAn understanding of basic statistics
will provide you with thewill provide you with the
fundamental skills necessary to readfundamental skills necessary to read
and evaluate results section inand evaluate results section in
published paperspublished papers

10. Are groups comparableAre groups comparable!!!!!!
 the baseline characteristics of thethe baseline characteristics of the
groups being studied should begroups being studied should be
comparablecomparable
 If not, they should be adjusted forIf not, they should be adjusted for
differencesdifferences

11. statistical testsstatistical tests
 Are they frequently used tests!!Are they frequently used tests!!
 If not, why!!If not, why!!

12.  Are the data analysed accordingAre the data analysed according
to the original protocol?to the original protocol?

13.  Was follow- up complete?Was follow- up complete?
Patients lost to follow-upPatients lost to follow-up………………loss ofloss of
subjects biassubjects bias
> 10% - 15 %> 10% - 15 % ……………………………………..invalid..invalid
resultsresults

14. P valueP value
 A P value of <0.05 means that thisA P value of <0.05 means that this
result would have arisen by chanceresult would have arisen by chance
on less than one occasion in 20on less than one occasion in 20

15. Standardization of measures of outcomeStandardization of measures of outcome::
Odds and odds ratioOdds and odds ratio
The odds is the number of patients who fulfilThe odds is the number of patients who fulfil
the criteria for a given endpoint divided bythe criteria for a given endpoint divided by
the number of patients who do not.the number of patients who do not.

16. For exampleFor example
the odds of diarrhoea during treatment with anthe odds of diarrhoea during treatment with an
antibiotic in a group of 10 patients may be 4antibiotic in a group of 10 patients may be 4
to 6 (4 with diarrhoea divided by 6 without,to 6 (4 with diarrhoea divided by 6 without,
0.66);0.66);
in a control group the odds may be 1 to 9in a control group the odds may be 1 to 9
(0.11). The odds ratio of treatment to control(0.11). The odds ratio of treatment to control
group would be 6 (0.66÷0.11).group would be 6 (0.66÷0.11).

17. Risk and relative riskRisk and relative risk
The risk is the number of patients whoThe risk is the number of patients who
fulfil the criteria for a given end pointfulfil the criteria for a given end point
divided by the total number of patients.divided by the total number of patients.

18. For exampleFor example,,
the risk of diarrhoea during treatmentthe risk of diarrhoea during treatment
with an antibiotic in a group of 10with an antibiotic in a group of 10
patients may be 4 to 10; in the controlpatients may be 4 to 10; in the control
group the risks may be 1 to 10. Thegroup the risks may be 1 to 10. The
relative risk of treatment to controlrelative risk of treatment to control
group would be 4 (0.4÷0.1).group would be 4 (0.4÷0.1).

19. C.IC.I
 The confidence interval around aThe confidence interval around a
result in a clinical trial indicates theresult in a clinical trial indicates the
limits within which the "real"limits within which the "real"
difference between the treatments isdifference between the treatments is
likely to lie,likely to lie,
 hence the strength of the inferencehence the strength of the inference
that can be drawn from the resultthat can be drawn from the result

20. Example:Example:
95 %95 % CI for RRR 25 % :CI for RRR 25 % :
 sample size 100sample size 100………………………….= -- 38 % to 59.= -- 38 % to 59
%%
 Sample size 1000Sample size 1000…………………….= 9 % to 41 %.= 9 % to 41 %
The larger the sample size , the narrower andThe larger the sample size , the narrower and
more precise the CI , and the greater ourmore precise the CI , and the greater our
confidence that the true RRR is closer toconfidence that the true RRR is closer to
what we have observedwhat we have observed..

21. OR = 0.34, 95% CI 0.23 - 0.52
• Odds Ratio < 1  decreased risk
• Confidence Interval does not cross 1  statistically significant

22.  A statistically significant result mayA statistically significant result may
not be clinically significant.not be clinically significant.

23.  The results of intervention trialsThe results of intervention trials
should be expressed in terms of theshould be expressed in terms of the
likely benefit an individual couldlikely benefit an individual could
expect (for example, the absoluteexpect (for example, the absolute
risk reduction)risk reduction)

24. How large was the treatmentHow large was the treatment
effecteffect??
Treatment effectTreatment effect………………………….. Adverse.. Adverse
outcomeoutcome
e.g.;e.g.;
Risk of outcome without therapyRisk of outcome without therapy
( baseline risk )( baseline risk ) XX ( = 20 % or 0.20 )( = 20 % or 0.20 )
Risk of outcome with therapyRisk of outcome with therapy YY ( =( =
15% 0r 0.15)15% 0r 0.15)

25.  Absolute risk reduction= X -- YAbsolute risk reduction= X -- Y
0.20-0.15= 0.050.20-0.15= 0.05
 Relative risk ( RR )= Y / X = 0.15 /0.20 =Relative risk ( RR )= Y / X = 0.15 /0.20 =
0.750.75
 Relative risk reduction ( RRR ) =Relative risk reduction ( RRR ) =
{ X -- Y/ X } x 100 % = 0.05 / 0.2 x{ X -- Y/ X } x 100 % = 0.05 / 0.2 x
100%= 25 % i.e :100%= 25 % i.e :
therapy reduced the risk of the outcome by 25therapy reduced the risk of the outcome by 25
% relative to that occurring among the% relative to that occurring among the
controlscontrols

26. the greater the RRR, the morethe greater the RRR, the more
effective the therapy.effective the therapy.

27. Example: M.IExample: M.I
 patients receiving medical treatmentpatients receiving medical treatment
have a chance of 404/1324=0.305 orhave a chance of 404/1324=0.305 or
30.5% of being dead at 10 years.30.5% of being dead at 10 years.
 Let us call this riskLet us call this risk xx. Patients. Patients
randomised to coronary arteryrandomised to coronary artery
bypass grafting have a chance ofbypass grafting have a chance of
350/1325=0.264 or 26.4% of being350/1325=0.264 or 26.4% of being
dead at 10 years. Let us call this riskdead at 10 years. Let us call this risk
yy..

28. RRRR
 The relative risk of deathThe relative risk of death——
 that is, the risk in surgically treatedthat is, the risk in surgically treated
patients compared with medicallypatients compared with medically
treated controlstreated controls——isis
 y/xy/x or 0.264/0.305=0.87 (87%).or 0.264/0.305=0.87 (87%).

29. RRRRRR
 The relative risk reductionThe relative risk reduction——that is,that is,
the amount by which the risk ofthe amount by which the risk of
death is reduced by the surgerydeath is reduced by the surgery——isis
100%-87% (1-100%-87% (1-yy//xx)=13%.)=13%.

30. ARRARR
 The absolute risk reduction (or riskThe absolute risk reduction (or risk
difference)difference)——that is, the absolutethat is, the absolute
amount by which surgical treatmentamount by which surgical treatment
reduces the risk of death at 10 yearsreduces the risk of death at 10 years
——is 30.5%-26.4%=4.1% (0.041).is 30.5%-26.4%=4.1% (0.041).

31. NNTNNT
 The number needed to treatThe number needed to treat——howhow
many patients need coronary arterymany patients need coronary artery
bypass grafting in order to prevent,bypass grafting in order to prevent,
on average, one death after 10 yearson average, one death after 10 years
——is the reciprocal of the absoluteis the reciprocal of the absolute
risk reduction: 1/ARR=1/0.041=24.risk reduction: 1/ARR=1/0.041=24.

32. ConclusionConclusion
 to be able to effectively conductto be able to effectively conduct
researchresearch
 to be able to read and evaluateto be able to read and evaluate
journal articlesjournal articles
 to further develop critical thinkingto further develop critical thinking
and analytic skillsand analytic skills
 to know when you need to hireto know when you need to hire
outside statistical helpoutside statistical help