Research methodology and biostatistics
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Transcript of Research methodology and biostatistics
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Dr. Raham BachaUltrasound specialistMD, PhD ScholarMSc Ultrasound (Gold Medalist) Lecturer Afro-Asian Institute Lahore
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Research Methodology &
Biostatistics.Respected readers it is mandatory for every researcher to know somewhat about research and biostatistics. But unfortunately we have been teach by biostatisticians in
our universities and medical schools. They want to make us biostatistician and teach us thoroughly. I
therefore felt a need to prepare a lecture in condense form which make enable us to know those terms which
are frequently used in research results.The purpose of the lecture is to read and understand some research and even analyze your research data and make inferences with the help of SPSS [email protected]
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What is Research?• Research is composed of two worlds.“Re” mean again
And Search mean to find new facts
It means to search again new facts or To modify older ones, in any branch of knowledge.
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Webster international Dictionary proposed a very inclusive definition.“A careful inquiry or examination in seeking facts or principles, diligent investigation in order to ascertain something.”Crawford Says: “Research is simply a systematic and refined technique of thinking, employing specialized tools, instruments & procedures in order to obtain a more adequate solution of a problem than would be possible under ordinary means.”
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It starts with a problem, collects data (facts and figures) analyses these critically based decisions of actual evidence. It evolves original work instead of mere exercise of personal opinion (theory). It is quantitative and measurements is therefore a central feature of it.
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• Don’t appreciate the research of other and yourself.
• Develop critical thinking.• Specialized tools and instruments
(Material i.e. data sheets)In fact research is treated as advancement in knowledge acquired through scientific methods
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Research provides:1. Analytic framework for subject
matter investigation2.Establishes relationship between
different variables e.g. cause and effect relationship, Co-relationship between variables.
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Important points• Research should not be treated as a
place of compilation work. It is not simply the compilation of material taken from different books and sources. It is always expected to something original that advances some knowledge.
• Research should be very clear in Researcher mind that he is going to do.
• The domain of Research problem must be clear.
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STATISTICSnumerical facts in any field of study. It concerns with collection, organization, summarization, analysis and drawing inferences from a data set. the science comprising methods, which are used in collection, presentation, analysis, and interpretation of numerical data (information).
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Bio-statistics
Bio-statistics is the branch of statistics that concerns
with the applications of statistical methods to
medical and biological data.
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In medical field, statistical methods enable us to
check the effectiveness of different testing
modalities in medicines. Recently, it has been
found that applications of statistical methods in
medical data are very effective. Testing of
hypothesis, analysis of variance, chi-square, non-
parametric methods, regression and correlation,
logistic regression etc. are frequently used in the
analysis of health and medical data.
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Being medical students often we need to
study research paper or we need to present
our research work in statistical terms. It is
therefor needed to know some of the
fundamental terms frequently used in
research papers.
Significance of Bio-Statistics in Medical.
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Central Tendency
Central tendency is a characteristic of a data set
which relates to its average value.
Most commonly used measures are,
Mean
Median and mode
Quartiles
Deciles
Percentiles
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MEAN
The most commonly used measure of central tendency. It is
the sum of all the observation divided by the number of
observation is mean.
nsobservatioofnumbertotalsetdataofnsobservatiotheallofsum
Mean
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Median
The median of a set of data arranged in order of
magnitude is the middle most value.
Mode
Mode is the most frequently occurring number in the data
set.
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Rates
The number of events in a population in specific time.
Suppose, in a specified population “n” events occur
during a fixed period of time n(A). If n(A) of these events
possess some characteristic, say A, then rate of the event
having the characteristic A is given by
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Prevalence Rate (P.R.)
Prevalence rate of an attribute or event in any group, is the
proportion of individuals in the groups having that
attribute at one point in time. This is also known a
prevalence ratio.
Kgroupinsindividualofnumbertotal
timegivenaatdiseaseorattributewithsindividualofnumberRP .
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Incidence Rate (I.R.)
The risk of developing the disease over a period of time is
called incidence rate and is calculated as:
K
groupinsindividualofnumbertotaltimegivenaatofdiseasecasesnewofnumberRI .
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Measures of Dispersion
The measure of spread of data/observations from its
averages. Statistical measures of dispersion are used to
measure the extent to which individual observations
disperse or cluster around the average. two commonly
used measures are;
range and
standard deviation.
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Range
Range is the difference between maximum and minimum
values of data set
Standard Deviation
The most widely used and stable measure of dispersion is
the standard deviation. This is a square root of variance.
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The most pleasurable moment of my life, when I was awarded with Gold medal
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Share feelings with media.
Dr. Raham Bacha Ultrasound Specilist
The Statistical Profile
25
The Statistical Profile
These include;
1. sensitivity,
2. specificity,
3. positive predictive value, and
4. negative predictive value.
5. accuracy,
6. reliability
Dr. Raham Bacha Ultrasound Specilist 26
These terms are defined as follows:
1. Sensitivity (True Positive Ratio or Rate):
The ability of a test to find disease when disease is present.
2. Specificity (True Negative Ratio or Rate):
The ability of a test to indicate no disease when there is no disease
present (i.e. to exclude disease when a patient is normal.
3. Positive Predictive Value (PPV):
PPV is a measure of how likely it is that disease is actually present
when the test result is positive. In other words, it is the proportion
of people with a positive test who actually have the disease.
Dr. Raham Bacha Ultrasound Specilist 27
These terms are defined as follows:4. Negative Predictive Value (NPV):
NPV is a measure of how likely it is that disease is actually
absent when the test result is negative. In other words, it is the
proportion of people with a negative test who are free of disease.
5. Accuracy:
The ability of a test to give the correct answer.
6. Reliability:
Consistency in obtaining similar results in similar
circumstances.
Dr. Raham Bacha Ultrasound Specilist 28
The Chi Square Test
This test brings together the statistical terms discussed
above. In the Chi Square, data from any test is compared
to data obtained using the gold standard. In graphical
form, the Chi square looks like this:
Dr. Raham Bacha Ultrasound Specilist 29
The Chi Square Test
Gold Standard result
Our testing modality result
present +
absent +
Positive +
A B
Negative -
C DDr. Raham Bacha Ultrasound Specilist 30
The Chi Square Test
Formulas for statistical terms:
1. Accuracy = (A+D)/ A+B+C+D
2. Sensitivity = A/ (A+C)
3. Specificity = D/ (B+D)
4. Positive Predictive Value = A / (A+B)
5. Negative predictive value = D/ (C+D)
Dr. Raham Bacha Ultrasound Specilist 31
Chi Square Example
Let’s take a few moments to work through an example using
the Chi square.
Suppose 100 non-invasive vascular tests were performed in
the vascular lab on patients who also had an arteriogram
(considered the gold standard in this case). The non-invasive
test yielded 55 positive results and 45 negative results. Of the
55 positive tests the arteriogram found 5 to be negative and of
the 45 negative tests, the arteriogram found 10 to be positive.
Dr. Raham Bacha Ultrasound Specilist 32
Chi Square Example
Let’s create a Chi square to illustrate the data above.
NON- INVASIVE VASCULAR TEST
Gold Standard present
+absent + Total
Positive + 50 5 55
Negative - 10 35 45
Total 60 40 100
Dr. Raham Bacha Ultrasound Specilist 33
Chi Square Example
The chart above illustrates the results of the 100 tests performed on our
patients.
Note that the 55 total positive exams by the non-invasive test are broken
down to indicate the ones with which the gold standard agreed and
disagreed.
Also note that the total of all four squares must equal the total number
of tests performed (i.e. 100 in our example.
Now let’s perform the calculations required for each of the six statistical
formulas discussed previously.
(Multiply the results by 100 in order to arrive at a percent.)
Dr. Raham Bacha Ultrasound Specilist 34
Chi Square Example
Accuracy = (A+D)/A+B+C+D
= (50+35)/50+5+10+35
= 0.85 x100
= 85%
Dr. Raham Bacha Ultrasound Specilist 35
Chi Square Example
Sensitivity = A / (A+C)
= 50/(50+10)
=50/60
= 0.83
= 0.83x100
= 83%
Dr. Raham Bacha Ultrasound Specilist 36
Chi Square Example
Specificity = D/ (B+D)
= 35/ (5+ 35)
= 35 / 40
=0.88
= 88%
Dr. Raham Bacha Ultrasound Specilist 37
Chi Square Example
Positive predictive value = A/ (A+B)
=50/ (50+5)
= 50/55
=0.91
= 0.91 X 100
= 91%
Dr. Raham Bacha Ultrasound Specilist 38
Chi Square Example
Negative Predictive Value = D/ (C+D)
= 35/ (10+35)
= 35/45
= 0.78
= 78%
Dr. Raham Bacha Ultrasound Specilist 39
Test Goals
The purpose of any of the non-invasive tests discussed in this
course is to identify disease when it is present and exclude it when
it is absent. Whether we are in Search of atherosclerosis or venous
thrombosis, we strive to produce the most accurate result within
our capabilities. In order to confirm or dispute the results of non-
invasive tests, our results are often compared with an established
diagnostic test known as the gold standard. In cerebrovascular
diagnosis, the current gold standard is the angiogram. In the study
of vascular disease, the venogram is still the gold standard.
Dr. Raham Bacha Ultrasound Specilist 40
Test Goals
The predictive value of a positive or negative test result is
perhaps the most useful expression of accuracy as far as
the referring physician is concerned. It is essential that we
remember that the skill of the vascular technologist may be
crucial in attaining accurate test results. I am sure that is
why we all study so hard to become excellent in the
performance of our examinations.
Dr. Raham Bacha Ultrasound Specilist 41
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Who knew that statistics could be this much fun!
Dr. Raham Bacha 43