Rerearch Design Ass.Prof.Dr - PowerPoint Presentation

Slide1

Rerearch Design

Ass.Prof.Dr

.

Baydaa

Hameed Abdullah

Slide2

Definition

A study design is a specific plan or protocol for conducting the study which allows the investigator to translate the conceptual hypothesis into operational one.

Study design is the plan

for

collection

of data to answer the

research

question.

Slide3

What does

research design

do?

Helps take decisions about how to complete the entire research:

Validly

Objectively

Accurately

Economically

Slide4

Functions of Research Design

1. The

identification and/ or development of procedures

and

logistical arrangements required to undertake a study

2. Ensuring that the procedures are adequate in quality to obtain valid, objective and accurate answers to the research questions.

Slide5

Classifications of Study Designs

Three types of classifications

on the basis of:

The number of contacts with the study population

The reference period of the study

The nature of the investigation

Slide6

Classifications of Study Design

Slide7

Slide8

r

Slide9

Advantages of descriptive studies

They

use

already available

data.

They

are less expensive and less

time-

consuming.

They

describe

the

pattern

of

disease

occurrence.

They

formulate research

hypothesis.

Slide10

Case reports

Researcher(physician) who see

unusal

preentation of a common desease and he describes the findings of this case,case

description may take any relevant description of the finding.

An unusual case may add to our Knowledge for example MI in very young person without ECG findings is unusual presentation of MI.

Slide11

Case series(clinical series)

When a group of cases of the disease are reported, but in this study we can not:

*Study the aetiology of the disease

*

T

esting the hypothesis

* Have a control group

But in the study it can help in generating hypothesis

Example: vaginal cancer is very rare in young females if 10 cases were reported and studied it may help us to generate a hypothesis when we interrogated with

stilbestrol

taking during pregnancy among their mothers(this

canbe

done by further studies)

Discovery of AIDS was a case series

Many

clincal

studies are case series

Slide12

Advantages of case reports or case series

Use available clinical

data

Detailed individual

data.

Add

to

our

knowledge.

Suggest need for

investigation (hypothesis

generation).

Slide13

Disadvantages

of case report or

case series

1.

May reflect experience of

one

person or one

clinician.

2.

No

explicit(clear)

comparison group.

Slide14

Ecological

Studies:

based on

studying

of a

group

of

people

not

individual as in

previous studies.

Correlation

data represent average

exposure level rather than

individual

level so we do

not

have each person

information

Ecological

studies

can

generate

a

hypothesis and need further confirmation

, it

provides

just initial

clues

to

causation

Example : as

meat consumption in

different

countries increases prevalence of

ca colon increases ,

Cigarette smoking increases ca lung prevalence increases as

well

Slide15

Advantages

of Correlational

Study

They

describe

the

disease in the

entire

population in

relation to

the

factor

of

interest.

They

use

the

correlation

coefficient

(r)

to

measure the

association

between the two

variables

of

interest.

They

are easy

to do,

inexpensive and can be conducted

quickly.

They

represent

the first

step in

searchingfor

exposure-disease

relationship (generate

hypothesis)

They

use available

data (administrative

or other aggregate

data).

Slide16

Disadvantages of correlational

study

Correlation data represent average exposure level rather than actual individual values. Data on exposure and data on outcome are collected

independently.

No

assurance

that

persons with exposure

(risk factor) of

interest are

the

same ones with outcome (disease)

of

interest.

Inability

to

link

exposure with the disease in particular

individual.

What

is

missing: relationship between exposure and outcome

at the

individual level

(incomplete

design)

Slide17

Cross-Sectional

studies

(prevalence

studies or surveys)

Cross-sectional:

where

only

ONE

set of

observations is

collected

at a

certain point

in time, disregarding the length

of

time

of

the study

as

a whole

It is a study

of

a

group of

people

at

a

point

in time for the prevalence of a disease or an

attribute

in a well

defined

population

but

data is

collected at

individual levels.

In this study

the measurements of exposure and

effect are made at

the same time . In cross-sectional studies,

we are looking

for both exposure and

outcome

Slide18

Study Design based on

no. of

contact with the population

Cross Sectional Studies:

One-shot or Status studies:

One time contact

Most commonly used design in social sciences

Obtain overall picture

Very

simple

design:

Decide what you want to find out about, identify the study population, select a sample and contact your respondents to find out the required information

Slide19

Advantages

of cross

sectional

study

Provide generalization from

the

sample

to

the population.

They

are

short

term studies and

not expensive.

Provide good information

for the

health

problems and good

for

health planners

to

assess health care

needs.

Used

for

generating hypothesis to be

test in

further studies.5.

Adapted

to chronic diseases

Slide20

Slide21

Disadvantages

1

.It

is di

f

fi

c

ult

to

s

e

pa

r

ate

cause

and

e

f

fe

ct

1-

because

measurement of exposure and disease are made at one point of

time

and

it is

impossible to

determined which

came first.

2-

Cases detected are prevalent cases (survivors)

leading to survival

bias cases cured or

died are not

detected.

Slide22

Possible

measurement error;

not

suitable for

rare

conditions;

Non response and

this will

affect

the

representation

of

the

sample.

Not adapted

to

incidence measurement

6.Not adapted to

severe

/

acute

diseases

Slide23

A

case control

study

Begins with the

selection

of

cases(diseases)

which

should represent

all

cases

from a

specified population.

The most difficult

task

is to select

controls

(people with no disease) the

controls

should

represent people who would have been

designated study

cases if they had developed the

diseases.

Slide24

Case control

study

An

important

aspect of this

study

is the

determination

of the start

and duration

of

exposure,

the

exposure status is

usually

determined after

the development of

the disease (retrospective) and

usually

by direct questioning

of the

affected person. Exposure may be

determined by biochemical measurement, established recording

system.

Slide25

Case control

study

Disease

Contro

l

s

Ex

p

o

s

ure

?

?

Retrospective

nature

Slide26

Sources of

selection of cases

in

case

control study

Hospital-based

case

control study:

the cases

will

be identified from

the

hospital or other health care

facilities.

These are

common, relatively

easy

and

inexpensive.

Population-based case control

study:

It involves locating and

obtaining data from all affected

individuals or a random sample from population.

Slide27

Selection

of

controls

in case

control study

It is

the

most

difficult

aspect of

Case

Control

Study (CCS), it

depends

on:

Characteristics and sources

of

cases.

Need to

obtain comparable

and

reliable information from cases and controls.

Practical

and economic

considerations.

Slide28

The

control should be comparable

to

the

source

of the

population

of

cases.

Any

exclusion

or

restrictions

made in the

selection

of

cases should be applied equally

to

the controls and vice

versa

.

Slide29

Advantages:

Suitable

for rare

diseases

.

Results can obtained

quickly.

Relatively

inexpensive and short term

study

Small sample

size

Available

data

No

ethical

problem

Slide30

Disadvantages

of

case control

studies

Incidence or

absolute

risk cannot

be

determined directly

from a case

control

study.

Temporal

relationship exposure-disease

difficult to

establish

Difficulty

in

selection

the

control.

Case- control study rely

upon retrospective data which lead to recall

bias.

Because the data are collected after

Can not use to

establish prevalence

b

e

wh

ethe

r

(

ret

ros

pec

ti

vel

y) i

t

is d

iff

icu

lt

to correlation is causal or

not.

5.

Slide31

Cohort Study:

(

follow up

study,

prospective ,

panel

study,

longitudinal,

incidence)

Follow

up

study

or

incidence study

Begin with a

group

of people (a

cohort) free

of

disease, who are

classified into subgroups according to exposure to

potential cause of disease, and the whole cohort is followed up to see how the subsequent development of new cases of the disease

differ between the groups

with and without exposure, cohort study

is a longitudinal study cohort study provides the best

information about the causation of disease

and the direct measurement of the risk of developing disease.

Slide32

Cohort

study

Identify

group

of

Exposed subjects

Un exposed

subjects

Measure

incidence of

disease

Compare incidence between

exposed and unexposed

group

Slide33

Population

Dis

e

a

s

ed

Exposed

Non-diseased

Diseased

Not exposed

Non

-

di

sease

d

T

ime

Direction of

inquiry

Figure shows cohort study

design

C

o

h

o

rt

Slide34

Experimental Design

The researcher

introduces the intervention

that

is

assumed to be cause of change

and

waits until it has produced or has been

given sufficient

time to produce the change.

The independent variable can be

observed , introduced, controlled or manipulated

by the researcher.

Slide35

An experimental study can be carried out in either a ‘

controlled’ or a ‘natural

’ environment.

Study population in a ‘controlled’ situation:

such as a

room

.

Study Population in a ‘natural’ situation,

population is in its

natural environment

Slide36

Blind Studies

In a blind study, the study population does not know whether it is getting real or fake treatment or which treatment modality.

The main objective of blind study is to

isolate the

placebo effect

: the psychological effect

Usually applied to studies measuring the effectiveness of a drug or treatment.

Slide37

Double- Blind Studies

Concept similar to that of a blind study

except that it also tries to

eliminate researcher bias

by concealing the identity of the experimental and placebo groups from the researcher.

Neither the researcher nor the study participants know who is receiving real and who is receiving fake treatment or which treatment model they are receiving.

Slide38

THANK YOU