
Research Methods Library of Alexandria
Questions and Answers
Q20 by Afiamaa (Mar 28,2015)
What are methodological assumptions?
Answer:
A20 by Faina Linkov (Mar 28, 2015)
That's a tough question as different types of study methodologies generally have different underlying assumptions.
Overall most investigators would have assumptions pertaining to the underlying distribution if data, study heterogeneity, and characteristics of targeted population.
This is a good article for case control and cohort studies description
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2998589/
You may comment to clarify the question
Q19 by Aliaa (Feb 1,2015)
What are the best conditions and the best prophylactic therapy that could be used to protect the experimental rats in a longterm (2 months duration) or chronic diabetes Study using Streptozotocin(STZ)? Is it suitable to use antimicrobial therapy as a prophylactic during such experiments? Is there any reference mentioned that issue?
Answer:
A19 by Ronald LaPorte (Feb 12, 2015)
Thank you very much for your question. I am a diabetes researcher, but sadly not working in the area of animal models. When I have an important question like this I search google scholar for others who have published in the area. Then select 510 and write to them posing your question. Typically a few will respond as scientists like to help colleagues. Then you can also continue to ask questions of that person. If no one responds, write to another 10. You will find someone who can help. Good luck!
Q18 by Joel Samson Ruvugo (Mar 31,2014)
I am in need of finding support on how to publish the literature review and what procedures to follow.
Answer:
A18 by Ronald LaPorte (Mar 31, 2014)
I am in need of finding support on how to publish the literature review and what procedures to follow.
Writing a literature can be a daunting task. Luckly most of the areas where one would need to write a literature review you can find example. Search first on your topic in google scholar, and google it self. From these you can identify review articles that provide information. It is best to do a systematic review. Do a search on Systematic reviews and this will provide guidelines. You might consider a Meta Analysis. We have a wonderful lecture on Meta Analysis in the supercourse
I personally like to do reviews and put tables which describe the literature. For example something like this.
Studies examining the relationship of Physical Activity to bone density. With tables like this one can immediately see the overview of the area. The text would then describe the area.
Author Year Population Type of study relationship between PA and BD conclusions comment
If you have not written a review before it is good to find a mentor. You can find mentors at your university, also you can find people who have published in the area and ask them to mentor you. In general it will be difficult to get a full professor to help. However, if you find an assistant professor who wants to help, contact them.
I would also do a search in Youtube on "how to write a review". I have been finding that many of the points presented in youtube are very good
The end of the review will typically consist of types of research that can be done in the future.
It is best initially to do reviews in areas that are specific to where you live. For example a review on the epidemiology of sand Pneumonia would be of interest to many people in and out of Saudi Arabia.
After your article is written search around to find experts who could review it.
Q17 by Naresh T Chauhan (Mar 31,2014)
I am helping one of my student on conducting one study on factors delaying the diagnosis of breast cancer in tertiary care center. Kindly guide me How to proceed? I mean after doing review of literature I found that most of the researcher had taken the newly diagnosed cases from hospital for particular duration, Is there any other way to select the subject in this study. This study will be done amongst three special center diagnosing and providing treatment to cancer pt.
Answer:
A17 by Ronald LaPorte (Mar 31, 2014)
A difficulty for me is that it is not really clear as to what your hypothesis is, and what you want to test. I typically have my students outline the hypothesis first, before defining the population.You appear to want to look at those how are late diagnosis compared to early. There is a large literature on this which you should review. Do a search in Google Scholar.
You can set up a study by identifying those who come in late compared to those who are early. You need to define operationally what "late" is, and what "early is". You could look at all women coming in during a certain period of time and do a case control study. There are many different types of surveys that you can use, use something that has already been used. You have to define your questions first as to what factors might be associated with a delay in coming in, then this will define your survey. It would be good also if you contacted people world wide who have done research in the area. It is an important area, but you need to do a little more homework as to how to set up the design
A17 by Nicolas Padilla (Mar 31, 2014)
Depend of study design.
Maybe Cases (Breast cancer with delaying diagnosis, por example metastasis) Controls (breast cancer with early diagnosis). And to ask or to see the registry why diagnosis was delayed (from subject, hospital, system etc)
A17 by Jay M. Fleisher (Mar 31, 2014)
The control group selected is problematic (CaseControl Methodology).
It ignores Length Bias and Lead Time Bias.
If one looks at a group Dx with early stage Ca vs Late Stage Dx one would be ignoring the aggressiveness of the individual cancers.
For example One person could be diagnosed with a early stage Ca and survive say, 8 years. While another person could be Dx at the same stage and only live one year.
The latter case having a more aggressive form of tumor.
I am confused at the outcome of the proposed study. Is it Survival. If so things like stage, and grade have to be factored in and one have to follow the cohort for at least 5 years. This puts us into a Prospective Cohort Design, which is costly.
The proposed study is more complex than it seems. One needs to Google both Lead Time Bias and Length Bias to better understand
Q16 by Mohammad Asif Alokozai (Mar 07,2014)
We have conducted the EPI coverage survey, and analyzed the data, the survey is WHO 30*7 cluster survey and the clusters select using PPS. The none response were calculated to be 20 percent, so we have had 30 clusters in each province with 210 interview to be done for each province, but now some province got lesser number of interview e.g. 159, or 166, 169, so does this data need reweighing during analysis? for finding the proportions of coverage using Stata software so what will be the best command to be used?
Answer:
A16 by Eman Eltahlawy (Mar 7, 2014)
If your cluster , 159 166 , or 169 , we must look for reasons why we are not get all out sample size if they take all children in this cluster and they are less than we planned so u not in need to reweigh but if there is some difficulties like security or refusal may be u must try again to approach this area and get what u missing , but if it is difficult so reweigh this areas only.
In cluster sample if the cluster become less than expected in some area you must revise why it become less.
First if cluster include all children in area and they are few in number as in some villages in the desert so you not need for reweigh. Second reasons if there is a refusal to participate or security condition at time of visiting those cluster so you may revisit this cluster to get the rest of target. Third if there is a big difficulties to reach those cluster again so you should reweigh those cluster again.
A16 by Nicolas Padilla (Mar 7, 2014)
First, you should know why the surveys are lesser than expected.
Second, in a clustered sampling all people in the cluster should be
included, may be including under 18 years.
Comment:
C16 by Mohammad Asif Alokozai (Mar 9, 2014)
Yes the reason for not getting the complete number of interviews in some clusters were because of less number of children in these clusters, not refusal or security. As security were the problem but we have recruited the interviewers from local area who were familiar with context and local traditions. For less number of interviews as total per province, although the number of interviews were more; but these participants were above or lower in age, of set criteria for the survey (children of 12 to 23) months. So this was the reasons for lower number of interviews.
Q15 by Dr Rajeev Rao Eashwari (Mar 02,2014)
I am a medical doctor in charge of eHealth services for a province in South Africa. I am planning to do a province wide teleHealth needs of rural health practitioners. I am struggling to get a survey tool for teleHealth needs analysis with an aim to have focus group interviews. Please advise
Answer:
A15 by Faina Linkov (Mar 3, 2014)
There was an article published on telehealth needs assessment a few years ago, it can be found here. I wanted to emphasize the fact that it's is important not just to assess the needs but also to keep in minds capabilities of the country for which you are trying to assess the needs. Professionals may say that they need extremely high level of expensive technology, but its important to remember that we need to look at what can be done with even limited technology.
Q14 by MB (Dec 05,2013)
Animal bite(dog bite or petty  home dog) is an important problem in my city ant I want investigate causes(factors that make animal angry and then animal,
attack their owner. How can I design the study(what study design I can use)? Is the questionary available for this study? (See Question 7 and Answer 7 too)
Answer:
A14 by NP (Dec 6, 2013)
You can use a crosssectional design. Search homes with dogs or domestic pets and ask for bites and risk factors (people battered the pet, diseases of the pets etc. Classify the homes in bites by dog or without bites and classify with risk factors or without them and calculate Odds Ratio and Attributable Fraction in exposed.
Q13 by ZF (Dec 05,2013)
I am trying to analyze the timeseries data for Air pollution and cardiovascular diseases. I want to use Generalized Additive Model (GAM) for analysis.
I am unable to find any help in this regard. I have to adjust for weather variables and age and gender. Please provide some guideline and help.
Answer:
Q12 by Mary Mwangome (Oct 2, 2013)
I am planning to analyse a cohort database for the effect of half dose of drug x prophylaxis on deaths. Drug x is a prophylactic medication.
The cohort is about 6 years old. Patients received halfdose X daily then from 1 year ago, the dosing of drug X in this cohort was changed to full dose to conform to National recommendations.
My interest is in finding out if half dose is equivalent or inferior to full dose in preventing deaths.
My outcome of interest is mortality though I will have to deal with loss to follow up rates of up to 30%. This outcome is chosen because morbidity data has not been collected in a standardized way and prospective collection has cost implications.
The prescription of X was also not very standardized and adherence not measured.
These data quality issues are what make me think of an ecological study. May be compare deaths rate over time by amount of drug X dispensed or by number of drug X prescriptions in a year or other parameters.
This question I want to answer is very important but due to ethical reasons, I was not allowed to prospectively compare (leave older patients on half dose and start new patients on full dose).
My question now:

I am thinking ahead in terms of interpretation of the results I find? I am not sure how I would go about that if I choose the ecological design. I am also thinking of the time lag issue between dose changing and when to expect effect on death given that the outcome is not a very commonly occurring one.

I don.t know if stata can help me in handling this kind of analysis including controlling for various other variables may be at group level as well.

If you have smarter ideas on how I can approach this question using the data I have, kindly help me.
Answer:
A12 by Faina Linkov (Oct 6, 2013)
Main points for the answer:

Loss to follow up of 30% in 6 years is very good and typical for studies of this caliber.

Survival analysis might provide good approach for some of the data analysis.

Stata and sas can both do the analysis.
A12 by Jay Fleisher (Oct 6, 2013)
There are sampling issues in this study design but I don.t think their fatal. If I understand the design, you have a situation where the patients act as their own controls with respect to dosage. Thus you have paired data. I would break the paring and run separate analyses on each dose. I would try Logistic regression on each dose. This would control for any covariates you have.
In other words you can use mortality as your outcome variable and dose1 + covariates for dose 1 for your Independent variables and do the same analysis separately for dose 2. Then compare the odds ratios for each dose along with 95% Confidence Intervals and p values that the Logistic regression will provide to you. If the Confidence Intervals overlap then Dose would have no effect. As for the 30% Lost to followup I think a 70% followup rate is acceptable. STATA, and SAS can do this easily. You would have to report the weaknesses in design of course. The .wash out. period is of concern since there was none. I would give it a try anyway. My opinion is that if your results show a clinically significant difference among the Higher dosage you have an answer. If they do not then you have another answer.
Q11 by Naresh Chauhan (Sep 29, 2013)
What is the sampling technique to draw samples from urban slum to know their behaviour on particular health problems and service utilization?
Answer:
A11 by Jay Fleisher (Oct 6, 2013)
The following steps should be taken to insure an unbiased sampling:

Define the Population you want to sample. The inference of any analysis will go to this population

Define your basic Measure of Effect. Are you going to sample Homes, Individuals, etc

When step 1 and 2 are completed RANDOMLY sample.

Conduct Analysis
Q10 by Nagah Selim (Sep 23, 2013)
If I would like to study prevalence of a disease among clients attending phcc and I have a rough estimate on the monthly attendees, can I use this number as total population for calculating the sample size?
If I calculate the sample size and distribute it proportionally between the health centers and I will take all the attendees during a specified period of time, say 2 months, for data collection,
What do we call these from the sampling methodology point of view? Could we consider this as all population?
Answer:
A10 by Jay Fleisher (Sep 23, 2013)
If we assume alpha=0.05 and a margin of error = 5% the following sample sizes are
For a prevalence of
48% 
n=384 
38% 
n=363 
43% 
n=377 
This is for an unstratified analysis because we don't have info for a difference for males vs females... One should add in about 20% for nonresponders, if applicable.
I have added a link ( see attachment) that explains how to do it and calculates the sample size for you. One can alternate alpha, size of the margin of error to get different estimates...
As for the second question, if I understand it, the answer is no one can't assume it is the whole population. What you have is a sample that goes to pcc. Thus the inference will be to the clinic
See a link: http://www.polarismr.com/researchlifeline/samplesizecalculator/
Q9 by Nagah Selim (Sep 23, 2013)
How can I calculate the sample size if I would like to assess the prevalence of depression, anxiety and stress among school children. According to the literature the prevalence is 48%, 38% and 47%respectively and also the prevalence is different among male and female.
Answer:
A9 Javier Muniz (Sep 23, 2013)
 Your study aims at estimating a proportion in the population.
 You have to consider:
 How do I select the participants?: Sampling procedure
 How many participants should I select: Sample size (related to .a. to some extent).
 Assuming simple random sampling in .a., the sample size depends on:

Size of the population to which you want to infere the proportion that you will find in your study (sample).
Surprisingly, it is not very important (unless very small populations).

Any idea of what you expect to find? (48%, 38% and 47% in your case). 50% is the most demanding assumption (the one that will result in a bigger sample size). Use 50% and you will be safe (your prestudy estimate is very close to 50%).

What precision do I need? Or, how wide do I want the confidence interval of my estimate? A wide confidence interval is less precise than a narrow one. The narrower the confidence interval desired when presenting the results (better precision), the bigger the sample size.
Below find an output of a program that I use (EPIDAT, developed by Xunta de Galicia, Spain and O.P.S.)
Sample size and precision to estimate a population proportion
Size of the population: 
20000 
Expected proportion: 
50,0% 
Confidence level: 
95,0% 
Study design: 
1,0 
Precision (%) 
Tamano de muestra 
1,000 
6489 
2,000 
2144 
3,000 
1014 
4,000 
583 
5,000 
377 
6,000 
264 
7,000 
195 
8,000 
149 
9,000 
118 
10,000 
96 
What does this mean? For example, if you choose to aim at a precision of 2% (IT IS YOUR DECISION AS INVESTIGATOR) for the whole study, you will aim to include 2144 participants. At the end of the study you will be able to say: The prevalence of depression among school children is 50%, with a 95% confidence interval of 4852% (maybe it is not exactly 50%, but you will be pretty sure that the proportion in the population is somewhere between 48% and 52%). When considering subgroups, your precision will decrease because of smaller sample sizes available (for example, you may have around 1000 boys and 1000 girls and the corresponding precision in these subgroups will be around 3%).
NOTE: We have assumed simple random sampling (not always feasible when studying kids in schools). If other design is chosen this may affect the sample size (bigger samples will be needed, at least in theory).
It is plenty of free programs available to compute the sample size for different study designs. I recommend you EPIDAT 3.1 because it also have some other very useful procedure for tabulated data (http://www.sergas.es/MostrarContidos_N3_T01.aspx?IdPaxina=62715) There is a more recent version (4.0) that still does not completely substitutes the previous one.
A9 by Abu Zar (Sep 23, 2013)
The sample size, in this case, refers to the number of children to be included in the survey.
Step 1: Base Samplesize Calculation
The appropriate sample size for a populationbased survey is determined largely by three factors: (i) the estimated prevalence of the variable of interest . chronic malnutrition in this instance, (ii) the desired level of confidence and (iii) the acceptable margin of error.
For a survey design based on a simple random sample, the sample size required can be calculated according to the following formula.
Formula:
n=(t. x p(1p))/m.
Description:
n = required sample size
t = confidence level at 95% (standard value of 1.96)
p = estimated prevalence of malnutrition in the project area
m = margin of error at 5% (standard value of 0.05)
Example
In the Al Haouz project in Morocco, it has been estimated that roughly 30% (0.3) of the children in the project area suffer from chronic malnutrition. This figure has been taken from national statistics on malnutrition in rural areas. Use of the standard values listed above provides the following calculation.
Calculation:
n= 
(1.96. x 0.3(10.3))/0.05. 
n= 
(3.8416 x 0.21)/0.0025

n= 
0.8068/0.0025

n= 
322.72~323 
Step 2: Design Effect
The anthropometric survey is designed as a cluster sample (a representative selection of villages), not a simple random sample. To correct for the difference in design, the sample size is multiplied by the design effect (D).
The design effect is generally assumed to be 2 for nutrition surveys using clustersampling methodology.
Example: n x D = 323 x 2 = 646
Step 3: Contingency
The sample is further increased by 5% to account for contingencies such as nonresponse or recording error.
Example: n + 5% = 646 x 1.05 = 678.3 ~ 678
Step 4: Distribution of Observations
Finally, the calculation result is rounded up to the closest number that matches well with the number of clusters (30 villages) to be surveyed.
Thirty is the standard number of clusters established by the WHO Expanded Programme of Immunization (EPI Cluster Surveys). There is no statistically necessary reason to maintain exactly 30 clusters, and the number can be adjusted if there is a compelling motive for doing so
Example: Final Sample Size: N = 690 children.
The final sample size (N) is then divided by the number of clusters (30) to determine the number of observations per cluster.
Example: N . no. clusters = 690 . 30 = 23 children per village
General Rule: Standardized Sample Sizes for Nutrition Surveys
The following table provides the recommended sample size for various estimated levels of malnutrition, incorporating standard values for confidence level and margin of error. The final sample size includes the contingency percentage and is rounded to match well with a 30cluster survey.
P 
n 
n x D 
N 
(est. % malnutrition) 
(base sample size) 
(n x design effect) 
(final sample size) 
0.2(20%) 
246 
492 
540 
0.25(25%) 
288 
576 
600 
0.3(30%) 
323 
646 
690 
0.35(35%) 
350 
700 
720 
0.40(40%) 
369 
738 
750 
0.45(45%) 
380 
760 
780 
0.50(50%) 
384 
768 
810 
Note: If it is not possible to find an estimated prevalence of malnutrition for the project area, the recommended action is to set the sample size at 810.
When in doubt, set the sample size at 810.
See also my lecture on Sample Size Estimation  http://www.pitt.edu/~super1/lecture/lec50811/index.htm
Q8 by Shatabdi Goon (Aug 28, 2013)
If I lost my data from survey, which was used in SPSS program, how I will be able to find out the statistical
analysis without having those data(want to evaluate p value). Is it possible to get the p value from the direct result?
Answer:
A8 by Mohamed E. Salem (Sep 5, 2013)
You can use spss and organise ur data for 2*2 table as 0 1, 1 1, 0 0, 1 0 and put the count for each category as a third column .
Then go to data weight and weight your data by the count column
A8 by Eman Eltahlawy (Sep 4, 2013)
You can use Epicalac 2000 for tabulated data to evaluate the p value, this easy program and free in the net.
A8 by Nicolas Padilla (Aug 29, 2013)
You can use epidat (statistical software for free from Xunta de Galicia and PAHO) using tabulated data, for example.
Q7 by Mohammad Babaeeian moghaddam (Jul 19, 2013)
Animal bites are an important problem in my city and I want to investigate that.
How can I design the study (what study design I can use)? Any questionnaires are available for such studies?
Answer:
A7 by Nicolas Padilla (Jul 20, 2013)
First, are you meaning animals as dogs, for example?.
If you want to know the burden of animals bites it is better to use a crosssectional design,
if you want to know the risk factors for animals bites, it is better to use casescontrols design.
Q6 by Andrey Kuznetzov (Jul 08, 2013)
Is there any standard R function for calculation of a variance of probability distribution (not sample variance)? Thanks in advance.
Answer:
A6 by Jay Fleisher (July 21, 2013)
I think the question pertains to the software package R. There are many
distributions besides the Normal Distribution.
I think the question is how to find the variance using R of a certain probability distribution.
I attach a brief description of what I think this question means.
FITTING DISTRIBUTIONS WITH R
Q5 by Hanan Abdulghafur Khalil (Jun 23, 2013)
May I ask about the required sample size for pilot study and pretesting and
whether the results should be mentioned briefly after the study completed?
Answer:
A5 by Jay Fleisher (Jun 23, 2013)
Sample Size calculations basically deal with the difference you expect to see and the
probability you wish this difference will occur ( Alpha).
There are many Sample Size calculators of the Web for free.
A5 by Nicolas Padilla (Jun 23, 2013)
In a pilot study you need about 1020% of the sample size needed for the larger study.
A5 by Fatma Hassan (Jun 23, 2013)
Baker (1994) found that a sample size of 1020% of the sample size for the actual study is a reasonable number
of participants to consider enrolling in a pilot study. Another rule of the thumb is to take 30 patients or greater to
estimate a parameter (Browne, 1999). Yes the results of pilot should be reported, better in the methodology section.
The details of any modifications in the questionnaire based on pilot should be reported.
A5 by Eman Eltahlawy (Jun 23, 2013)
Thanks Dr Hanan for your question. It depends on your needs  to test the language of questionnaire,
the methodology and logistics inside the field and to ensure that time needed for questionnaire.
Q4 by Murtada Osman (Jun 11, 2013)
How to select the journal for publication?
Answer:
A4 by Deena Alasfoor (Jun 14, 2013)
Selecting a suitable journal for publication is one of the most difficult tasks of researchers.
The impact factor; interest of the journal and the value of your manuscript; as well as your experience in
publishing all count for this. Obviously, you would want to aim at the journals with the highest impact factors.
However, it is very hard to publish in these unless your manuscript is of great importance; and you have collaborators
who have published in that area earlier. First, select the journals that might interest you; probably these will be the ones you refer to them.
If your publication is context free; then you might have a better chance in publishing in an international high impact factor.
If your manuscript for example presents national survey results you may want to go to a national or regional journal.
Once you have read the authors guide carefully, be sure that your paper matches the journals subjects of interest;
then if you have a number of these you could try for the highest impact factor first, and then if rejected go to the lower one
until your paper is accepted. This could happen at the first time; but could also take some attempts before getting a journal
that accepts your publication. Sometimes the topic had been discussed enough, and the authors do not see that your publication
adds a new thing to the existing knowledge, do not get disappointed, keep trying.
Good Luck
A4 by Eugene Shubnikov (Jun 11, 2013)
I will recommend you to study Supercourse lecture
http://www.pitt.edu/~super1/lecture/lec48271/index.htm
with the name "Publishing research articles: a look on the inside" by Sholpan Askarova.
For your first paper please consider sending your article to Journals with not the highest impact factor as Sholpan recommends.
Q3 by Saad Tai (Jun 2, 2013)
I am interested to conduct a KAP study on HIV in Pakistan among medical doctors.
My question is from where I can get questionnaire or how can I make self made questionnaire.
Answer:
A3 by Bruce G. Weniger (Jun 8, 2013)
Search the medical literature for wellwritten, highquality reports in competitive journals for
studies with similar research questions and methods you wish to employ.
Many journals are already making available questionnaires, protocols,
and other studyrelated documents by optional online download of “supplementary”
material for published “printed” reports.
For example, the supplementary material to this study
(http://dx.doi.org/10.1056/NEJMoa1202541) is available in the “Tools”
section at right on its webpage, providing a URL link to the additional files:
http://www.nejm.org/action/showSupplements?doi=10.1056/NEJMoa1202541
If the questionnaire is not thus posted, then you can email or write to the paper’s author(s),
explaining that you would like to perform a similar study in your own population, using similar questionnaire for comparability.
Ask if the author(s) will provide you the questionnaire to adapt for your own study.
Offer to acknowledge their assistance in your future paper, and to cite their work if relevant to what you eventually perform and find.
A3 by Shacara Johnson (Jun 8, 2013)
You can access information on KAP (Knowledge, Attitudes, and Practice) survey instruments using the World Health Organization’s
website or conduct an internet search for HIV KAP surveys in Pakistan. You might also want to search publications by fellow researchers
who conducted similar research among HIV care providers in Pakistan and contact them about
collaborating or asking for permission to utilize their instrument for your work.
There are several references to HIV KAP instruments pertaining to the Eastern Mediterranean region (which would include Pakistan)
stemming from topics ranging from conducting behavioral surveillance of risk factors to countrylevel
results of KAP implementation. If you cannot identify a current instrument being used in Pakistan,
then you might seek to search for other KAP instruments used in a similar setting for
which you can modify for what you desire to examine in Pakistan among health care providers.
Two sources as examples from the WHO site that may be of interest to provide points of consideration while constructing your instrument
include: http://applications.emro.who.int/dsaf/dsa1232.pdf (HIV surveillance)
and http://whqlibdoc.who.int/publications/2008/9789241596176_eng.pdf
(A guide for developing KAP for control but may be useful as you are developing your instrument for HIV).
A3 by Deena Alasfoor (Jun 7, 2013)
Guideline on how to do a KAP study is on the following link:
http://whqlibdoc.who.int/publications/2008/9789241596176_eng.pdf
The research questions depend on the context and how you want to use the information; in general;
It is important that each knowledge question is followed up with an attitude and a practice question that helps you in the course of action/intervention .
As a researcher you need to identify your questions,
based on the context and use the KAP method to explore these.
I hope this is helpful.
Q2 by Abdelrahim Mutwakel Gaffar (May 19, 2013)
I am conducting an evaluation study for a project using "a pre intervention  post intervention" design.
What is the best statistical test to examine the change due to the intervention.
Answer:
A2 by Mohamed E. Salem (Jun 13, 2013)
If you want to measure the impact of an intervention, the simplest test are

The paired sample Ttest; in case your indicator is measured quantitatively (blood sugar level, BMI, etc..).
See this link on how to perform paired sample Ttest using SPSS
http://www.youtube.com/watch?v=MJGk2sg4EZU

The McNemar test; If your indicator is measured qualitatively (diseased or not, complicated or not, etc…).
See this link on how to use McNemar
http://www.youtube.com/watch?v=k4kqp9S8WEw
My suggestion to you is to improve your study design (prepost) intervention design is a weak design if you want to relate
the change (improvement) to your intervention. Including a control group will give more strength to your results.
Random assignment of the cases and controls to your intervention will make your study even stronger and blindness will be perfect if it is applicable.
I am attaching a link to study designs
http://www.socialresearchmethods.net/kb/destypes.php
In case you operate one of the above designs the analysis should be more indepth using, double difference analysis,
regression model and nonequivalent group design in case of quasiexperimental designs
A2 by Jay M. Fleisher (Jun 10, 2013)
If your data is continuous and Normally distributed you can use a paired
ttest Procedure. This would apply if you can create an index over all questions.
If you data is Categorical you can use McNeamars Test. This would be
applicable if you are looking at individual questions
Remember your data are pared.
A2 by Rami H. AL Rifai (Jun 9, 2013)
The idea is that "Tell what the type of the dependent variable you have to tell you what type of test you could use".
There are 2 main types of variables:
 Continuous like measuring blood pressure.
 Discreet: like Yes or No variables.
Those variables could be dichotomous (two subcategory) or dichotomous (three subcategories) or even more than three subcategories.
However, in pre post intervention studies, the testes to be used if your intervention was carried on the same groups are different from those if your intervention was carried out on different groups like control and intervention groups.
For example, if your dependent variable is continuous, and your intervention was on the same group,
you have to use Paired Ttest to detect if there was a difference due to intervention or not.
But before that you have test the assumption of normality distribution for the
dependent variable otherwise you have to use the nonparametric test.
A2 by Nicolas Padilla (Jun 6, 2013)
If the variable is quantitative, the mean of differences (measure 1  measure2)
then the mean of differences and then t Student (short sample size less than 50) or Z(sample size more than 50).
A2 by Sami AR ALDubai (Jun 6, 2013)
Someone can use SPSS. The statistical test depends on the type of the dependent variable someone want to test.
If the dependent variable is normally distributed then you can use "paired sample TTest". If it is not normally distributed,
then you can use the alternative nonparametric test "2 related samples" (Wilcoxon Signed Ranks).
A2 by Shacara Johnson (Jun 5, 2013)
This research would be considered a repeated measures study design or paired design,
in which you are interested in observing an intervention change in the same group of subjects.
The statistical test to use is called a paired ttest so that you can determine whether a difference exist
(finding the mean and standard deviation of the differences between the before and after measurements)
and then the tdistribution for the single mean is used to analyze the difference (at the significance level).
A2 by Mohammad Babaeeian moghaddam (Jun 5, 2013)
If If we have a repeated measures design with prepost measure and the variables are distributed normally
(As assessed by SPSS, we can use a paired t test analysis. If the data are not distributed normally,
we can use a Wilcoxson nonparametric test. These two tests can be found in all standard statistical
testing procedures (SPSS, SAS and others).
Q1 by Nabil D Sulaiman (May 19, 2013)
What is the best sampling frame for a national diabetes prevalence study in the absence of updated GHS sample?
Answer:
A1 By Nabil D Sulaiman (May 26, 2013)
Various sampling approaches could be explored to seek the best possible sampling frame for a rapidly changing expatriate population in the Gulf region, which are, The National Census (GHS), Water and Electricity Register, Telephone register and National ID.
Based on representativeness and feasibility, we in UAE have adopted a novel sampling methodology, which involved systematic random sampling through Preventive Medicine Departments (PMDs), where all expatriate adults in the UAE are legally required to attend every 23 years to renew their residency visa. The PMD is a single place where recruiters, interviewers, nurses and phlebotomists are available. All staff working were nominated and trained for the study. Blood samples for both the study and the visa renewal, were collected at the same visit.
A1 By Mohamed E. Salem (May 25, 2013)
In the absence of General Household Survey (GHS) sample, the most accurate and easy alternative is to use the readily available country geographical information to create your own national representative sample. The country map including its geographical information will be used as the sample frame. Geographical Information System (GIS) applications will help you to divide your map into representative clusters of households. ArcGIS is one of the application that could be used to do this exercise.
Here is a youtube link for ArcGIS tutorial http://www.youtube.com/watch?v=3BkaazSVIbI
Here is an alternative youtube link (in Arabic) the sound is not very good http://www.youtube.com/watch?v=FR28TMbs98
The program will enable you to use your country map as a sample frame. Using the geographical information available on the map, you can select the clusters of households. Within each cluster you can draw a systematic random sample using walk through method inside the selected study areas.


