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CHM 371 #6

RESEARCH METHODOLOGY

Asst.Prof.Dr. Kanda Wongwailikhit

Objective

Student should be able to...

1. distinguish between an observational study and

a designed experiment

2. Differentiate the sampling method

(2)

Observational Studies

Observational Studies

An observational study measures

the characteristics of a

population by studying individuals in a sample

does not attempt to

manipulate or influence the variables of interest.

A designed experiment study will

applies a treatment to

individuals (referred to as experimental units or

subjects)

attempts to isolate the

effects of the treatment on a response variable.

Designed Experiments

(3)

Visit this link from Science Daily, from July 8th, 2008.

This was a tricky one. It was actually an observational study. The key is that the researchers didn't force the veterans to have PTSD, they simply observed the rate of heart disease for those soldiers who have PTSD and the rate for those who do not.

This was a tricky one. It was actually an observational study. The key is that the researchers didn't force the veterans to have PTSD, they simply observed the rate of heart disease for those soldiers who have PTSD and the rate for those who do not.

http://www.sciencedaily.com/releases/2008/07/080707081834.h tm

EXAMPLE 1

EXAMPLE 1

It talks about the relationship between Post-Traumatic Stress Disorder (PTSD) and heart disease.

(4)

Visit this link from the ,

EXAMPLE 2

EXAMPLE 2

If you were thinking that this was an observational study, you were right!

The key here is that the individuals sampled were just asked what was important to them. The study didn't try to impose certain conditions on people for a set amount of time and see if those conditions affected their responses.

If you were thinking that this was an observational study, you were right!

The key here is that the individuals sampled were just asked what was important to them. The study didn't try to impose certain conditions on people for a set amount of time and see if those conditions affected their responses.

http://www.gallup.com/poll/10806 7/Fuel-Prices-Now-Clearly-America ns-No-Concern.aspx

It looks at what Americans' top concerns were at that point. Do you think this was an observational study or a designed experiment? Why?

(5)

This last example is regarding the "low-carb" Atkins diet, and how it compares with other diets.

Read through this summary of a report in the New England J. of Med.

Can you figure out whether it's …

(a) observational study

(b) a designed experiment EXAMPLE 3

EXAMPLE 3

As expected, this was a designed experiment, but do you know why? The key here is they forced individuals to maintain a

certain diet, and then compared the participants' health at the end.

As expected, this was a designed experiment, but do you know why? The key here is they forced individuals to maintain a

certain diet, and then compared the participants' health at the end.

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There are 3 major types of observational studies

1. cross-sectional studies,

2. case-control studies

3. cohort studies.

Types of Observational Studies

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Cross-sectional Studies

Cross-sectional studies don't give very strong results. In above

example, we can't be sure that those working with asbestos who don't report cancer won't eventually develop it.

This type of study only gives a bit of the picture, so it is rarely used by itself. Researchers tend to use a cross-sectional study to first

determine if their might be a link, and then later do another study (like one of the following) to further investigate.

Cross-sectional studies don't give very strong results. In above

example, we can't be sure that those working with asbestos who don't report cancer won't eventually develop it.

This type of study only gives a bit of the picture, so it is rarely used by itself. Researchers tend to use a cross-sectional study to first

determine if their might be a link, and then later do another study (like one of the following) to further investigate.

study involves collecting data about

individuals at a certain point in time.

A researcher concerned about the effect of working with asbestos might compare the cancer rate of those who work with asbestos versus those who do not.

EX

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Cross-sectional Studies scheme

(9)

Case-control Studies

Case-control studies are frequently used in the medical community to compare

individuals with a particular characteristic (this group is the case)with individuals who do not have that characteristic (this group is the control).

A control group is a group in an experiment

that is under normal conditions. If one was

testing out fertilizer, the control group would

be a plant with just normal dirt.

(10)

Case-control Studies (cont.)

One of the most famous examples of this type of study is the “ link between smoking and cancer”.

almost 80% of adults in the UK were smokers, and the connection between smoking and lung cancer had not yet been established.

Doll and Hill interviewed about 700 lung cancer patients to try to determine a possible cause.

2

This type of study is retrospective, because it asks the individuals to look back and describe their

(11)

Case-control Studies scheme

(12)

Cohort Studies

Cohort Studies

A cohort describes a group of individuals, and so a cohort study is one in which a group of individuals is selected to participate in a study. The group is then observed over a period of time to determine if

particular characteristics affect a response variable.

Based on their earlier research, Doll and Hill began one of the largest cohort studies in 1951. The study was again regarding the link

between smoking and lung cancer. The study began with 34,439 male British doctors, and followed them for over 50 years. Doll and Hill first reported finding in 1954 in British Med. J., and then

continued to report their findings periodically afterward. Their last report was in 2004, in British Med. J., . This last report reflected on 50 years of observational data from the cohort.

(13)

This last type of study is called

prospective

,

because it begins with the group and then

collects data over time.

cohort studies

are definitely

the most powerful

of the observational studies, particularly with

the quantity and quality of data in a study like

the previous one.

Cohort Studies (cont.,)

(14)

Cohort Studies scheme

(15)

A study concerning dementia and "mid-life ills".

Researches followed more than 11,000 people over a period of 12-14 years. They found that smoking,

diabetes, and high blood pressure were all factors in the onset of dementia.

EXAMPLE 4 EXAMPLE 4

What type of observational study was this? (a) Cross-sectional

(b) case-control (c) cohort?

(16)

In 1993, the National Institute of Environmental Health

Sciences funded a study regarding the possible relationship between radon levels and the incidence of cancer.

The study gathered information from 413 participants who had developed lung cancer and compared those results

with 614 participants who did not have lung cancer.

This study was retrospective - gathering information about the group of interest (those with cancer) and comparing them with a control group(those without cancer). This is an example of a case-control study.

EXAMPLE 5 EXAMPLE 5

(17)

Thought his may seem similar to a

cross-sectional study, it differs in that the individuals

are "matched" (with cancer vs. without

cancer)and the individuals are expected to look

back in time and describe their time spent in the

home to determine their radon exposure.

(18)

In 2004, researchers published an article

regarding the relationship between the mental

health of soldiers exposed to combat stress. .

EXAMPLE 6

EXAMPLE 6

Since this was simply a survey given over a short period of time to try to examine the effect of combat duty, this was a cross-sectional study. Unlike the previous example, it did not ask the participants to delve into their history, nor did it explicitly

"match" soldiers with a particular characteristic.

What type of study was this? (a) Cross sectional study (b) Case control study (c) Cohort study

The study collected

information from soldiers in four combat infantry units either before their

(19)
(20)

The goal of the cross-sectional study is a better

understanding of the disease and risk factors that are associated with the disease.

The retrospective study is good to get an estimation of the potential risk factors and usually these relationships are confirmed by the prospective studies.

Therefore, the retrospective study is less valid than the prospective method.

The results from these studies have been utilized for

(21)
(22)

Types of sampling

Non-probability samples

Probability samples

Probability samples are the best

Ensure

RepresentativenessPrecision

Probability of being chosen is unknown Cheaper- but unable to generalise

(23)

Non probability samples

Convenience samples

Snowball sampling

Purposive sampling

(24)

Convenience samples

(ease of access)

sample is selected from elements of a population

that are easily accessible

Man a street interview

Teacher use students

Asking the one you meet at a supermarket

Volunteers

Snowball sampling

(friend of friend….etc.)

(25)

Quota sample

Researcher uses some knowledge of the

population to build some representativeness into the sampling plan

Divides population into different strata and

samples from each of them

Usually better than just convenient

Purposive sampling

(judgemental)

You chose who you think should be in

the study

(26)

QUOTA sampling

(27)

Methods used in probability samples

Simple random sampling

Stratified sampling

Systematic sampling

Cluster sampling

(28)

Simple Random Sampling

Simple Random Sampling

A sample of size n from a population of size N is obtained through simple random sampling if every possible

sample of size n has an equally likely chance of occurring.

write everyone's name on a slip of paper and draw two from a hat

(29)
(30)

http://www.youtube.com/watch?v=yx5KZi5QArQ

http://www.youtube.com/watch?v=YamE4KqCv3k

(31)

Randomized Controlled Trial

(32)

Simple random sampling

Using excell

(33)

=RANDBETWEEN(1,24)

=RANDBETWEEN(1,24)

=VLOOKUP(B3,E$2:F$26,2)

(34)
(35)

HOME WORK for 6

th

class

Use excell program for simple randomized

name of xxxxxx(your patients, school) etc.,

Population > 50 name

(List of name your self)

Sampling for 25% of population

Send to kanda@rsu.ac.th

Email subject : CHM371 random-student ID

HOME WORK for 6

th

class

Use excell program for simple randomized

name of xxxxxx(your patients, school) etc.,

Population > 50 name

(List of name your self)

Sampling for 25% of population

Send to

kanda@rsu.ac.th

(36)

Stratified Sampling

Stratified Sampling

Stratified sampling is different. With this technique, we separate the population using some characteristic, and then take a proportional random sample from each.

A stratified sample is obtained by separating the population into non-overlapping groups

(37)

Stratified Sampling

(38)

One easy example using a stratified technique

would be a sampling of people at ECC.

To make sure that a sufficient number of

students, faculty, and staff are selected, we

would stratify all individuals by their status -

students, faculty, or staff. (These are

the

strata

.)

Then, a proportional number of individuals

would be selected from each group.

Example 1

(39)

Systematic Sampling

Systematic Sampling

For our starting point, we pick a random number between 1 and k. For our visual, let's suppose that we pick 2. The individuals sampled would then be 2, 5, 8, and 11.

(40)

Systematic Sampling

Systematic Sampling

(41)

Systematic sampling works well when the individuals are already lined up in order.

In the past, students have often used this method when asked to survey a random sample of students.

Since we don't have access to the complete list, just stand at a corner and pick every 10th* person walking by.

Systematic Sampling (cont.,)

(42)

Cluster Sampling

Cluster Sampling

Cluster sampling is often confused with stratified sampling, because they both involve "groups". In

(43)

Begin with names of population

Insert code the characteristic Select column  data  sort chose sort by

OK

(44)
(45)

Excell program for systematic sampling

Begin with names

Calculate interval from N/n and round off to integer

Set chosen number to begin

First + N/n

(46)

Cluster Sampling

Cluster Sampling

A cluster sample is

obtained by selecting all individuals within a

randomly selected

collection or group of individuals.

In essence, we use cluster sampling when our

(47)

Cluster sampling

Section 4

Section 5 Section 3 Section 2

(48)

One situation where cluster sampling would apply might be in manufacturing.

Suppose a company makes light bulbs, and would like to test the effectiveness of the packaging. You don't have a

complete list, so simple random sampling doesn't apply, and the bulbs are already in boxes, so you can't order them to use systematic.

And all the bulbs are essentially the same, so there aren't any characteristics with which to stratify them.

To use cluster sampling, a quality control inspector might select a certain number of entire boxes of bulbs and test each bulb within those boxes. In this case, the boxes are the clusters.

Example 3

(49)

Multistage Sampling

Multistage Sampling

Often one technique isn't possible, so many professional polling agencies use a technique

called multistage sampling. The strategy is relatively

self-explanatory - two or more sampling techniques are used.

(50)

Stage 1: A quality control engineer removes every 200th box coming off the line. (The plant produces 5,000 boxes daily. (This is systematic sampling.)

Stage 2: From each box, the engineer then samples three packages to inspect. (This is an example

of clustersampling.)

Let's suppose that the bulbs come off the assembly line in boxes that each contain 20 packages of four

bulbs each. One strategy would be to do the sample in two stages:

Multistage Sampling (cont.,)

(51)

HOME WORK for 7

th

class

Use excell program for

1. stratified sampling

2. systematic sampling

(use your previous names)

Send to kanda@rsu.ac.th

Email subject : CHM371 strat+system

-student ID

HOME WORK for 7

th

class

Use excell program for

1. stratified sampling

2. systematic sampling

(use your previous names)

Send to

kanda@rsu.ac.th

(52)

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