Dr. Jaddou - Research Designs

7/28/2019 Dr. Jaddou - Research Designs

1/36

Research Designs


2/36

Is it true that hypertension and diabetes are widelydistributed in community X?

Is it true that hypertension and diabetes are increasing incommunity X?

Are obesity, positive family history and sedentary lifepositively associated with hypertension and diabetes?

I think that antibiotics are not effective in acute tonsillitis. I dont believe that smoking is a CVD risk factor.


3/36

Related research:

The three communities-based survey

Blood pressure profile of school children and adolescents,

Jordan Hypertension and associated factors among a recently

urbanized community

Hypertension and associated factors among a Bedouincommunity in North Jordan


4/36

1. Survey Designs

1.1 Purpose (objective) of Survey Research

1.1.1 Description

Making descriptive assertions about some population;e.g. data from previous studiesprovide information on thedistribution of certain attributes among the target population; age,

sex, and level of education

Discovering the distribution of certain traits or attributes.

The researcher is not concerned with why the observeddistribution exists, but merely what that distribution is.

researcher often describes sub samples and compare them.e.g. distribution of patients with DM, HBP, controlled anduncontrolled hypertension among age and sex groups.


5/36

1.1.2 Explanation In studying hypertension, for example, the researcher may

wish to explain why some people develop hypertension whileothers do not.

An explanatory objective almost always requiresmultivariateanalysis


6/36

1.2 Unit of Analysis (UA)

Typically, the UA for a survey is a person, but it could befamilies, hospitals, or health centers.

Data are collected to describe the individual units ofanalysis;

Those descriptions are aggregated and manipulated in orderto describe the populationrepresented by the units ofanalysis.

There could be more than one UA in a survey.

UA has to be identified in advance.


7/36

1.3 Basic Survey Designs

Once the objectives of survey and its unit of analysis areidentified, the researcher has several different surveydesigns to choose from.

A. Cross sectional surveys

B. Longitudinal surveys.


8/36

A. Cross-sectional Surveys

Data are collected at onepoint in time from a sampleselected to describe some larger population at that time.

Such a survey can be used for description and forexplanation.


9/36

B.Longitudinal Surveys

Data are collected at different points in time, on a sampleselected to describe some larger population.

Permit the analysis of data over time.

Theresearcher is able to report changes in descriptions andexplanations


10/36

Types of longitudinal designs:

a. Trend studies

b. Cohort studies.c. Panel studies


11/36

a. Trend studies

A given general population may be sampled and studied atdifferent points in time.

e.g. Jordan Population & Family Health Survey (JPFHS) on Ever-married women of reproductive age taken every 5 years.

Trend studies often involve data collection over a long period oftime.

Each time of data collection the sample and the generalpopulation are not the same .


12/36

B. Cohort studies.

A Cohort study focuses on the same specific

population each time data are collected, although the

samples studied may be different.e.g. a sample taken from 2010JUST Medical Graduates(cohort) and 5 years later another sample is drawn fromthe 2010 JUST medical graduates.

If 5 years later a sample was drawn from the 2015 JUSTmedical graduates we would have a trend study ofgraduating classes and not a cohort study of the 2010graduates.

A variant of cohort is a cohort study of a given age group(twenties-thirties.)


13/36

C. Panel studies

Panel studies involve the collection of data over time from thesame sampleof respondents.This sample is called panel

e.g.Silent gallstone study


14/36

The logic of survey sampling


15/36

Survey= Sample Survey vs. All members of populationsurvey (census).

Why Survey?1. Clearly less expensive.

2. Requires less time to complete the study.

3. Sample surveys are often more accurate than census.Why?


16/36

a. Census requires a very large staff of interviewers thusjeopardize the quality of data.

b. Interviewing all members of large population require alengthy interviewing period. Thus it would be difficult tospecify the timeto which the data refer.

c. The managerial requirement of a very large survey wouldbe far greater than normally faced survey researchers.


17/36

Types of survey methods

1. Probability sampling

2. Non-probability sampling.

Probability sampling is the most respected and useful method.

Why ? Population of individuals vs. population of platelets

heterogeneity vs. homogeneity


18/36

A sample of individuals from the population, must contain thesame variation as exists in the population.

A basic principle of probability sampling is the following: Asample will be representative of the population from which itis selected, if all members of the population have anequalchanceof being selected in the sample.

Although perfect representation is difficult to achieve yetprobability sampling offers two special advantages:


19/36

i. It is typically more representative than any other types ofsamples.

ii. probability theory permits researcher to estimate theaccuracy or representativeness of his sample


20/36

Sampling Concepts and Terminology


21/36


22/36

1. Element

An elementis that unit about which information is collectedand which provides the basis of analysis= unit of analysis.

2. Sampling Unit

A sampling unitis that element or set of elementsconsidered for selection in some stage of sampling.

In Single stage sample, sampling units are the same as theelements.

primary sampling units", "secondary sampling units", and"final sampling units" would be used to designate thesuccessive stages.

E.g sample of census blocks-sample of households from allhouseholds of selected blockssample of members from allmembers of selected households (elements)


23/36

3. Sampling frame

It is the actual list of sampling units from which thesample, or some stage of the sample, is selected .

Sampling frame define the survey populationE.g. (telephonedirectory, electricity bills, municipality's list of voters).

4. Observation Unit

An observation unit, or the unit of data collection, is anelement or aggregation of elements from which informationis collected.

e.g. heads of households (the observation units) to collectinformation about every member of the household (the unitsof analysis).


24/36

6. Variable

A variableis a set of mutually exclusive characteristicssuch as sex, age, employment status

N.B.: a variable, by definition, must possess a variation,otherwise it is constant.

7. Parameter

It is the summary description of a given variable in the

population.e.g. mean income, age distribution


25/36

8. Statistic

It is the summary description of a given variable in a

survey sample. Sample statistics are used to make estimates of

population parameters.


26/36

9. Standard Error

It is a measure of spread and indicates the extent towhich the sample estimates will be distributed around the

population parameter.

Probability sampling methods seldom, if ever, providestatistics exactly equal to the parameters that they areused to estimate. Probability theory, however, permits us

to estimate the degree of error to be expected for a givensample design.


27/36

Probability sampling theory The ultimate purpose of survey sampling is to select a set of

elements from a population in such a way that descriptions ofthose elements (statistics) accurately describe the totalpopulation from which they are selected.

Probability sampling provides a method for

- enhancing the likelihood of accomplishing this aim, and

- estimating the degree of probable success.

Random selection(equal chance) is the key for this process.

Computer programs/random tables are used to select arandom sample.


28/36

Types of sampling designs

1. Simple Random Sampling (SRS)

Start by establishing the sampling frame

Assign A number to each element

Use Tables of random numbers to generate the

sample

2 Systematic sampling


29/36

2. Systematic sampling

Start by establishing the sampling frame

Assign A number to each element, then

Every Kth element in the total list is chosen(systematically) for inclusion in the sample.e.g. to draw a sample of 1,000 from a list of 10,000 then every10th element will be selected.

Systematic sampling is superior to SRS in convenience ifnothing else.

Caution should be paid to the arrangement of the list.

3 Stratified Sampling


30/36

3. Stratified Sampling

Starts by organizing the population into homogeneoussubsets and to select the appropriate number of elementsfrom each.

The researcher insures that appropriate number ofelements is drawn from homogeneous subsets.

e.g. university students, may first be organized by college andappropriate number of first year, second year, third yearare

drawn. Has the advantage of reducing the standard error

4 Multistage cluster sampling


31/36

4. Multistage cluster sampling

Starts by sampling ofgroupsof elements-clusters;

listing of elements within each of the selected clusters.

Sample each list and then add them to form the studysample.

May be used when can not generate an exhaustive list ofthe target population.

involves the repetition of two basic steps: listing and

sampling.e.g. sampling school teachers.


32/36

Design the survey Instrument

The types of data to be gathered during the survey could be:

1. Information: age, education, whether the person hashistory of diabetes and so on. This kind of data is usuallygathered through an instrument called "questionnaire".

2. Physical measures such as blood tests, blood pressuremeasure, and measures of weight and height.


33/36

Data collection:

The data will then be collected using the above instruments(questionnaire, weighing scale, measuring tape, blood pressuremachine.


34/36

Data processing.Once collected, the data is then entered in the computer to

make a spread sheet file that contains all the data collected.

The data in the file are entered according to what is called"the coding manual".e.g. For instance males are given number "1" and females aregiven number"2.


35/36

Data analysis.

Using the statistical packages available to you, you can

Generate frequencies study variables, Perform t-tests, Chi squares, and any other statistical

analysis needed by the researcher.


36/36

Report findings.

The results that you generate out of the analysis will then betransformed into a report to be used by interested groups;scholars in the field, scientists, decision-makers, healthplanners, etc.

Documents

Dr. Jaddou - Research Designs