Letter to Editor
Sleep
Disordered Breathing in Pakistani population
I read with interest the
article by Haqqee et al on a hospital based preliminary report on Sleep Disordered Breathing in
Pakistani population published in J Ayub
Med Coll Abbottabad 2002;14(3):2-4.
Though
a very interesting and informative study, this writer also notes that the
nature of the studied sample should be clearly stated. A part of the statements
in the abstract section describes "… a
total of 123 subjects ----", while in the Material and Methods section
states that ‘consecutive patients
attending AKUH for an executive medical check-up during the months of August
and October 1998 were surveyed for their sleeping habits. All the patients
completed a sleep questionnaire. ----”
If
the study is based on 123 subjects in that particular period of time for
‘executive medical check up’, then actually it is not for any ‘patients’. The definition of
‘executive’ needs to be specified. It seems to suggest that this is
intended to be a descriptive study generalizable to
another specific population. The data are clearly not suited to that purpose.
Therefore it is not a good sampling of the Pakistani population as stated
on the title.
Regarding
the section of ‘Material and Methods’, there are some questions. How were the
patients selected? What was the process by which patients ended up in an
‘executive medical check up’ in the hospital?
All these questions deserve clearer answers.
As noted in the paragraph on statistics in the section of Material and
Methods: ‘ Statistical analysis was by chi square
test, t-test and Fisher’s exact test. A p-value less than 0.05 was considered
significant.’ the main analysis seems to be an estimation of prevalence of
snoring and sleep disordered breathing and the cross-tabulation of these two
conditions in a specific ‘executive medical check –up’ clinic of that specific
hospital-based population. But what does this mean and how does this
scientifically generalize to any other population, such as what has been stated
in the title of this article, namely “Pakistani
population”, especially when the non-executive portion of the
population with different age groups are considered?
As to the section of the “Result”
and “discussion” of this article, certainly just as the authors state that the
reported prevalence of sleep disordered breathing (SDB) varies in different
communities,1-3 these discrepancies have largely been ascribed to
the methodological difficulties in characterizing these syndromes in large
populations.4
This article is the first preliminary report that has evaluated the
prevalence of sleep disordered breathing in the
subjects in a specific population, who attended the AFUH clinic for executive
medical check-up for that particular period of time. The prevalence of snoring,
snoring with apnea, and snoring with apnea and excessive daytime sleepiness
(EDS) are found “very similar to those of Western studies that show a
prevalence of OSA as 9% for women and 24% for men----” 1, reported
by Young et al. It is worthwhile to note
that the one reported by Young, T. et al is from
There are about 12 major prevalence studies of obstructive sleep aponea (OSA)5 at
the time when this study was published. Most of them used a sleep questionnaire
followed by an evaluation of sleep disordered breathing by overnight polysomnography or oximetry. The
authors of this study have already humbly raised a critique for their own
methodology, which would state two important issues, firstly, they used only
the questionnaire and secondly, most published studies are drawn from large
populations, whereas this study used only their own executive ‘patients’ as a
sample of their own population. In
addition, this writer raises a third issue of the importance
of randomization of sample, as the randomized controlled trial is the
strongest research design for evaluating net effect of intervention, knowing
that there are limitations for randomized trial such as coverage for medical
payment, time and cost.6
With respect to the study according to Lugaresi
et al’s report, which was published in
1980, snoring has been a common phenomenon seen in about 20% of the adult
population, and in about 60% of men over 40 years of age 7. In this (Haqqee et
al’s) study, snoring was reported in 46% of the sample population of 123
subjects and tended to increase with advancing age. It is worthwhile to note that in this study
that the mean of ages for the snorers is 46.6±10.5, while that for non-snorers is 40±12.4 years old.
As a contrast, hypertension has been associated with obstructive sleep
apnea (OSA) in large population based studies,8
such as what was reported by Hla et al. Since
this association is independent of age, therefore the means of ages, which are
noted in this study, should not make any much discrepancy.
As noted in the section on Material and Methods, in this study
statistical analysis was by Chi square test, t-test and Fisher’s Exact
Test. Among these tests, t-test is the
simplistic one. With respect to Fisher’s Exact Test, it is a procedure that one
can use for data in a two by two contingency table. It is an alternative to the
Chi-square test in this study, since the total number of subject is 123, which
does not require Yates correction.
The Chi-square test relies on a large sample approximation. Therefore,
one may prefer to use Fisher’s Exact Test in situations where a large sample
approximation is inappropriate.
There is really no lower limit on the amount of data that is needed for
Fisher's Exact Test. One does have to
have at least one data value in each row and one data value in each column. If
an entire row or column is zero, then one does not really have any 2 by 2
table, which is not the situation in this study. On the other hand, Fisher's
Exact Test is also very useful for highly imbalanced tables. If one or two of
the cells in a two by two table have numbers in the thousands (which certainly
is not the situation in this study either), and one or two of the other cells
has numbers less than 5, one can still use Fisher's Exact Test.
Once decision has been made to use Fisher Exact Test,
such as in this study, whether a one or two tailed version may misrepresent the
statistical significance of data.
A uniform specification statement should be required in order to prevent such a
potential errors in interpretation.9-12 Unfortunately,
it appears that there is no such a statement found in the report of this study.
In summary, allow
this writer taking the liberty to congratulate the authors for their find
quality of effort in preparing this preliminary study, and certainly also looks
forward to reading their final study with inclusion of a more objective
evaluation of subjects’ symptoms and signs, an expansion to a larger sample
size without selection of subjects’ occupations and ages from the population 13,
and a specific statement of whether one- or two-tailed version when Fisher
Exact Test is contemplated.
Bing H. Tang, M D,
Master of Public Health,
Department of Medical
Education & Research
Email: drtang1942@yahoo.com
REFERENCES
1.
Young T, Palta M,
Dempsey J, Skatrud J, Weber S, Badr
S. The occurrence of sleep disordered breathing among middle-aged adults. N Engl J Med 1993; 328:1230-5.
2.
Mary SM, Lam B, Lauder IJ, Tsang KWT, Chung K, Mok Y, Lam W. A community study of Sleep Disordered
Breathing in Middle-aged Chinese Men in
3.
Ng TP, Seow A, Tan WC.
Prevalence of snoring and sleep related- breathing disorders in Chinese, Malay
and Indian adults in
4.
Lindberg E, Gislason
T. Clinical Review Article: Epidemiology of sleep-related obstructive
breathing. Sleep Med Rev 2000;4(5): 411-33.
5.
Davies RJO, Stradling
JR. The epidemiology of sleep apnea. Thorax 1996;51: (suppl
2): s65-s70.
6.
Rossi, Freeman. Evaluation. Fifth Edition.
7.
Lugaresi E, Cirignotta F, Coccagna G, Piana C. Some epidemiological data on snoring and cardiocirculatory disturbances. Sleep 1980; 3:221-24.
8.
Hla KM, Young TB, Bidwell T, Palta M, Skatrud JB, Dempsey J.Sleep apnea
and hypertension. A population based study. Ann Intern Med 1994;120:382-8.
9.
Jospeh L. Fleiss.
Statistical Methods for Rates and Proportions. Second Edition.
10.
11.
Brett J. Cassens.
Preventive Medicine and Public Health. Second Edition.
12.
David Knoke, George W.
Bohrnstedt. Statistics for Social Data Analysis.
Third Edition.
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Hulley, Cummings.
Designing Clinical Research.
Response of author
·
An executive referred to men/women which were
sent for annual complete routine medical check up to AKUH from their respective
Organisations. These were normal/healthy individuals
of the community and hence represented an appropriate sample for a preliminary
report. Selection was on a voluntary basis. We agree that a more appropriate
word should have been ‘participant’ rather than ‘patient’.
·
We have already pointed out in our discussion
that this was a limited sample which aimed at defining the magnitude of SDB in
Pakistani population and this needs to be expanded to include a bigger sample
size. We are currently looking at a much larger sample to further our
preliminary report.
·
We merely said that our preliminary data showed
similar trends of SDB as of Western population and no comparisons were made.
·
We must remember that it is a questionnaire
based data and lacks the objective evaluation to corroborate the statements
entered on the questionnaire and may actually be an underestimate of both
snoring as well as apnoea.
·
We note the valuable comments made by Dr Bing
regarding the analytical methods.
Dr Raana Haqqee
Consultant Physician, Department of Respiratory Medicine,
Email: raanahaqqee@hotmail.com