????????? Collection of Epidemiologic Data

1
?????????Collection of Epidemiologic Data

• ???,????,???????
• Bao-Ping Zhu, MD, MS
• ??????????????????
• U.S. Resident Expert Advisor to China FETP

2
???????????Types of epidemiologic data

• ???? Outcome data
• ???? Exposure data
• ??????????? Data on related risk factors

3
?????????Sources of epidemiologic data

• ???? Existing data
• ?????? Data to be collected

4
??????Examples of existing data

• ??????? Population data
• ?????? Census data
• ???????? Inter-census estimates
• ?????? Vital statistics data
• ???? Birth registry
• ???? Death data
• ??????? Marriage and divorce
• ???? Surveillance data
• ???? Disease surveillance
• ???????? Behavioral risk factors surveillance

5
??????Examples of existing data

• ????????? Health status and behavioral data
• ??????? Health and nutrition surveillance
• ???????? Behavioral risk factor surveillance
• ??????? Socioeconomic data
• ???????, ??????, ??? CPI, GNP, unemployment rate
• ?????? Administrative data
• ???? Outpatient records
• ???? Hospitalization data
• ??????? Laboratory testing data

6
??????????? Methods for collecting epidemiologic
data

• ?????? Self-administered questionnaire
• ????? Personal interviews
• ??????????? Biochemical analysis of biological
  specimens
• ???????????? Physical or chemical analysis of the
  environment

7
?????????Scales of Epidemiologic Data

• ???? Nominal
• ??,?? Gender occupation race/ethnicity
• ???? Ordinal
• ?????? Socioeconomic status low, medium, high
• ???? Interval
• ?? Temperature
• ???? Year of birth
• ???? Ratio data
• ?? Weight
• ?? Height

8
???????????Higher scale data are always preferred

• ???????? Richer information
• ??????? Higher statistical power
• ???????????? More options for statistical
  analysis
• ????????? Higher scale data may be transformed
  into lower scale data
• ??????????????? Lower scale data may not be
  transformed into higher scale data

9
???????????????? Data is only as good as the
measurement instrument used

• ??????????,??????????? We would like to measure
  the truth every time we measure a
  characteristic
• ?????????,????????? Any deviation from this
  constitutes a measurement error
• ???????????
• ??? Reliability
• ??? Validity

10
??? Reliability

• ???????????,?????????? Refers to the degree of
  similarity of information obtained when the
  measurement is repeated in the same subject
• ????????????? Is the same value arrived at every
  time the measurement is taken/made?

11
??? Validity

• ????????????? Is it a true reflection of what you
  want to measure?
• ????????,??????????????????,?????????? A measure
  lacks validity if an observer or an instrument
  measures the characteristic in the same
  individual repeatedly higher or repeatedly lower
  than the real value
• ????????????? This systematic error
  introduces a bias
• ??????????,?????????? A measure can be reliable
  but not valid

12

• ????????????
• Validity and Reliability

????? The Target metaphor

?? ????
?? ????
???? ????
??? ???
13
??????? The sources of error in measurement

• ???? The instrument
• ??????????????,????????????? The instrument
  itself gives different results for the same
  individual
• ??,?????????? e.g. blood pressure cuff
• ???? The observer
• ??????????? Inter-observer variation -
  differences among observers
• ?????????????? Intra-observer variation -
  differences in the same observer

14
??????? The sources of error in measurement

• ???? The subject
• ????????? Biological inconsistencies
• ???? Memory
• ?????? The environment
• ?? Temperature
• ?? Humidity

15
?? Questionnaires

• ???????????????? A good questionnaire takes time
  and effort to design
• ???????????!Dont underestimate this !!
• ??????????????????! The questionnaire should only
  collect that information that you need for the
  study
• ????,??,????? e.g. Demographics / Exposure /
  Outcome
• ???????????????????? Think about the research
  questions and analysis plan
• ??????????,??????????? e.g. Are you only
  interested in exposure (Y/N) or are you also
  interested in dose ??

16
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

17
??????????? State the Research Questions or
Hypotheses

• ???????????? Generate hypotheses to guide data
  collection
• ?????? Review descriptive studies
• ????????? Look and learn from outliers
• ????? Talk to people
• ??????????? Talk to local officials
• ??????? Go to field and study the environment

18
??????????? State the Research Questions or
Hypotheses

• ????????????????Think about questions and
  related outcomes in advance. For examples
• ????????? Contact with a case is associated with
  illness
• ?????????? Vaccine is associated with protection
  from illness
• ????????? Milk is associated with illness
• ??????????? Illness was associated with the
  amount of milk consumed
• ??????,????????????????? What exposures and
  outcomes do we specifically want to measure?

19
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

20
??????(???)Outline an analysis plan (empty
tables)

• ??????????What measure of association will be
  used?
• ????????????Which associations am I interested in?

??Ill
???Not Ill
????? Contact with case
???????????? We need to measure/define illness!
????? No Contact with case
????????? We need a measure of contact!
21
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

22
?????????Variables to be collected (observed or
measured)

• ???? The participant
• ????,???,??Participant (Name, ID )
• ??,??,??,??Address, age, sex, occupation, etc....
• ?? The exposure
• ??,??,??,??,????If/where/when/how much/how long
• ?? The outcome
• ??,??,???? Symptoms/signs/tests

23
????????????Information that may be collected
with a questionnaire

• ???? Individual characteristics
• ??,??,?? Height, age, income
• ?? Environment
• ????,????? Housing, family size
• ??,?? Behaviors, practices
• ??,?? Alcohol or tobacco consumption
• ?? Judgements
• ?? Opinions
• ?? Attitudes
• ??????? Indicators of knowledge
• ????????? Risk factors
• ?????????? Healthy lifestyle

24
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

25
????????? Methods of obtaining information

• ?????? Self-administered questionnaire
• ????? Mail (postal)
• ???? Web-based
• ???????? Monitored
• ????????? Interviewer-administered questionnaire
• ???? By telephone
• ????? In person

26
?????????What method to choose?

• ????? Nature of questions
• ??????????What is the research question to be
  addressed?
• ?? Convenience
• ????????Which method is most readily available?
• ?? Cost
• ??How costly is it to collect the information and
  how affordable is the method?

27
???????? Questionnaire administration

• ????? In-person interviewing
• ???????? Most frequently used
• ?????????? High response rates flexibility
• ???????????? Time consuming potential observer
  bias
• ???? Telephone interviews
• ?????????????? Inexpensive rapid large
  numbers or area
• ????????????????????????????? Non-response
  no visual cues rushed potential observer bias
• ????? Postal Questionnaires
• ???????????????? Inexpensive rapid large
  numbers or area
• ????????????? Non-response complexity

28
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

29
????? Types of Questions

• ?????? Factual
• ???,???,???? Demographic, laboratory, clinical
  information
• ????? Opinions and Attitudes
• ????????,??,??,???,?? Beliefs, ideas,
  predispositions, and values related to the topic
  under study
• ??,?? Information/knowledge
• ????????????(???????) Measures what people know
  (presence or absence of knowledge)
• ???????? Correct or incorrect knowledge

30
????? Types of Questions

• ?? Behavior
• ??????? Description of behavior
• ???????????????????? Difficult to evaluate how
  people think they behave vs. what they actually
  do
• ?? ???????????,???????????? Constructs
  responses to multiple questions are combined to
  estimate a particular variable
• ???????? Socio-economic status (SES)
• ?????? Quality of life
• ??????????? Self efficacy to change a behavior

31
??-????Measuring Dose-Response Relationship

• ????????????????
• ??????? ? ?? ? ?? ? ?? ? ??
• ????????? ? ?? ? ?? ? ?? ? ??
• ???????? ? ?? ? ?? ? ?? ? ??
• ????????? ? ?? ? ?? ? ?? ? ??
• ????????? ___?
• ???????????
• (?????????)????????,???????? ___?
• ???????????
• ?????????????,????????????
• ??????___??
• ??????___??
• ??????___??

32
???????????Measuring Dose-Response Relationship

• ?????????
• ???????,????????,????????
• ???????

33
????Aids to recall

• ?????
• ???????,?????
• ??
• ??????
• ??????
• ??????
• ??
• ???????
• ?????????(???,??)????

34
???????A hepatitis A outbreak
35
????11????????????????????????

• ??????????????
• ???????
• ????????
• ????3???????
• ?????????????

36
????????Ask Preference Questions

• ?????????
• ??(???)? ??? ??? ??? ??? ???
• ??? ??? ??? ??? ??? ???
• ???? ??? ??? ??? ??? ???
• ????
• ?????,???? ??? ??? ??? ????
• ????????,???????(???) ??? ?????????

37
???????????Common Problems

• ???? Ambiguous questions
• ????? Not self-explanatory
• ????????? Two questions in one (compound
  questions)
• ???? Complex words
• ????????? Asking things that people wont
  remember
• ????? Hypothetical questions
• ????????? Not enough categories
• ??,??????? Too long or too many ideas
• ??????? Overlapping categories
• ?????? Leading questions
• ?????????? Degree of accuracy not specified

38
????Questionnaire Solutions

• ??????? Simple language
• ???????? Closed questions
• ????????? Staged questions
• ??????? Scaling
• ?????? Visual clues
• ??? Pilot tests

39
????????Be clear about the data format you want!
????? Unspecified Format
??Date 12/10/06 10/12/06 06/10/12
?
?
?? Age 9 (?9???9???)(What? Years or months)
40
?????Format of questions

• ?????????? Closed format ? give a fixed
  response
• ????? Simple and quick easy to use in the field
• ??????????????? Reduces discrimination against
  those who are less literate
• ?????????????? Easy to code, record, and analyze
  results quantitatively
• ?????? Easy to report results
• ???????????? Limits the variety and amount of
  data collected

41
?????Format of questions

• ??? ?????? Open-ended format ? allows
  exploration of issues
• ?????????????,????????? When there is interest in
  what information a subject will volunteer before
  asking a specific response
• ???????,???????????When conducting qualitative
  research when verbatim responses are needed in a
  report
• ????????????????? Can be used even if a
  comprehensive range of alternative choices cannot
  be compiled
• ???????? Not easy to administer and record
• ????????????????? Difficult to code responses,
  analyze data, and quantify results

42
????? Open Question
??/???????? What milk products have you
eaten? ________________________
43
??????/?Closed question Yes / No
????????Did you have any of the following
symptoms ? ?Yes ?No ??? Unsure ??
Diarrhea ?? Fever ?? Abdominal pain ??
Vomiting ?? Other
44
??????Staged Questions

• ?????????????,?????Did you drink the apple juice
  at the party and how much did you drink?
• _______________
• ? OR
• ?????????
• Did you drink any apple juice?
  ?Y ??N
• ??,?????If yes then how much did you drink?
• 1?1 cup 2?2 cups 3?3 cups 4????4 cups

45

• ??????????
• Other Types of Structured Questions

????? Nominal response ????? What is the
patients gender? 1 ?male 2?
female ????? Ordinal response (useful in
ranking) ?????????????????,1??,5??? Please
rank the following food items in degrees of how
much you would like to eat with 1 being the
highest and 5 being the lowest? __ ??
Chicken __ ?? Beef __ ?? Horse
__ ?? Fish __ ?? Sheep
46
?????? Using Scales

• ????????? How would you characterize the pain
  that you had?
• ??Mild ?? Moderate ??Severe
• ? OR
• ?????????0-10?? How would you characterize the
  pain that you had on a scale of 0 to 10?

10
0
1
2
3
4
5
6
7
8
9
47
??????? Problems and Pitfalls

• ??????????????????????? Avoid questions that
  ask two things at once - you wont know which
  bit people are answering
• ????????????????/??
• e.g. Have you ever had neck pain and diarrhea?
  Yes/No?
• ???? Ambiguity.....
• ????????????
• e.g. Do you go to the toilet a lot?

48
??????? Problems and Pitfalls

• ??????Avoid jargon
• ????????????
• ????????????????
• ????????????
• ??????????????,????,???????????????
• ???????? Avoid options that are not mutually
  exclusive when they need to be
• ????? What age are you?
• 16-20 ?
• 20-25 ?
• 25-30 ?
• 35-40 ?

49
??????? Problems and Pitfalls

• ??????? Avoid leading questions
• ?????????????????Do you think that the food in
  the hotel made you sick?
• ?????????????????????Did the hotel staff seem
  unhygienic to you?
• ???????????????????? Do you agree that the
  hospital staff were close to exhaustion?
• ?????? Avoid making the questionnaire too long
• ????? Typographical / spelling errors
• ?????????
• ????????
• ??????????
• ???????

50
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

51
?????Sequence of Questions

• ??????????????? Group questions by topic or
  response options
• ???????? Question order is important
• ?????? General to particular
• ???? Easy to difficult
• ?????? Factual to abstract
• ?????????? Start with closed format questions
• ???????????????????? Start with non-threatening
  questions relevant to the main subject
• ?????????????? Dont put the most important item
  last

52
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

53
??????Layout General

• ????????? Particularly important with postal
  questionnaires
• ???? Attractive
• ?????????? Clear language and instructions
• ???? Easy to follow
• ?????????? Well illustrated jumps/skips
• ???????? Keep it short and simple

54
??????Layout General

• ?????? Practical tips
• ????????????? Make it easy for survey team
  members in the field
• ??????????? Keep form well-spaced and open
• ????????????? Make spaces for recording data
  obvious
• ?????? Each question needs to fit wholly on a
  page
• ????????? Make it easy for keypunching
• ?????? Place spaces for recording data
• ???????????????? Record data in consistent visual
  framework
• ??????????,?9?- Use common symbol for
  unknown "9", "Unk", "-", etc.

55
???? Layout example

• ?????????
• ????
• 1. ????_________ ????_________
  ????__________________
• 2. ?? ? ?? ? ? ? ?
• 3. ????12?????
• 1) __?, ?? ??2??????????? ? ? ?
• 2) __?, ?? ??2??????????? ? ? ?
• 3) __?, ?? ??2??????????? ? ? ?
• 4. ?? ? ???? ? ????
  ? ???
• ????????? ????? ? ????? ? ????? ? ??????
• ????
• 6. ??????????? ? ?? ? ?? ? ?? ? ??
• ?????????? ? ?? ? ?? ? ?? ? ??
• 7. ??????? ? ?? ? ?? ? ?? ? ??
• ????????? ? ?? ? ?? ? ?? ? ??
• ???????? ? ?? ? ?? ? ?? ? ??
• 8. ??????????? ? ?? ? ?? ? ?? ? ??
• ????????? ? ?? ? ?? ? ?? ? ??

56
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

57
??Translation

• ????????????? The best way to interview people is
  to address them in their own language
• ???????/????????????Researcher makes
  questionnaire in his language
• ????????? Translation into local language
• ????????????????? Back-translation (check)
• ???????????????? Interviewers should be fluent in
  the language of the interviewees

58
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

59
?????Training Interviewers

• ????? Need to understand the questionnaire
• ???? Terminology
• ?? Skips
• ?? Definitions
• ??????????,????? Only read the questions, not
  interpret them for the respondent
• ???????????? Master the consent process
• ????????????????,???????? Remove interviewer bias
  by asking everyone questions in calm,
  non-judgemental fashion

60
?????Training Interviewers

• ????????????????? Interviewers should be trained
  in all tasks required to conduct the interview
• ??????????? Find the household to interview
• ?????????,?????????? Approach people pleasantly
  and acquire consent
• ?????????? Assure confidentiality and anonymity
  (when possible)
• ????????,?????? Administer questionnaire, and
  respond to questions
• ??????,?????????? Review filled out questionnaire
  forms

61
??????????Steps in questionnaire design

• ??????????? State the research question(s)/hypothe
  ses
• ?????? Outline an analysis plan (empty tables)
• ?????????? List the variables to be measured
• ???????? Decide how the questionnaire will be
  administered
• ??????? Formulate the questions
• ??????Decide on the questions
• ????? Phrase the questions
• ??????? Determine the sequence of questions
• ???????? Plan the layout and design of the
  questionnaire
• ?????????????? Translate if necessary
• ????? Train interviewers
• ??? Pilot test

62

• ???????
• Why pretest questionnaires?

• ????????? Ease of understanding
• ????????? Avoid ambiguity
• ????????????? Identify other exposures
• ????????? Clarify response categories
• ???????? Eliminate unnecessary questions
• ????????? Understand sensitive issues
• ?????? Estimate time needed
• ???????????? Uncover logistical problems

63
???Pretest

• ?????????????,????????????? Administer
  questionnaire to other survey staff and correct
  questionnaires
• ???????? Go over each question
• ??????????Ensure questions are easily readable
• ?????????Be sure skip patterns clear

64
???Pretest

• ????????????????!Always pretest on target
  population
• ???????????? Supervisors should observe pretest
• ?????????????? Pretest entire data collection
  procedures
• ????????? Ask respondents about interview
  questions
• ???????? Ask survey workers about
• ???????? Individual questions
• ???????????? Entire process of data collection

65
?????????Pretest answers these questions

• ??????????????Are people willing to answer
  questions?
• ??????????????? Are people willing to allow
  specimen collection?
• ???????????Are any questions difficult to answer?
• ??????????Are any questions sensitive?
• ????????????Do people understand every question?
• ????????????Can interviewers follow instructions
  on data collection form?
• ??????????Are there other difficulties with the
  data collection form?
• ??????????Are there any answers that should be
  included on data collection form?
• ???????????????How long does data collection
  take?
• ?????????????,??????What is best organization of
  data collection steps within household?

66
??????Advantages of questionnaires

• ?????????????????????(????????)Can reach a large
  number of people relatively easily and
  economically (especially postal questionnaires)
• ???????? Provide quantifiable answers
• ???????? Relatively easy to analyze

67
??????Disadvantages of questionnaires

• ???????????? May provide only limited insight
  into the problem
• ???????????? Limited response allowed by
  questions
• ????????? You may not have asked the right
  questions
• ??????? Varying response
• ?????????????????? They may not understand your
  question and may interpret it differently
• ??????????? Postal questionnaires ? low response
  rate
• ?????,????????????? Hard to chase after missing
  data need to get it correct the first time

68
?????? Other Issues

• ????????????? Look at previously used
  questionnaires
• ????????????? Standard validated measurements
• ???? Ethics
• ????? Observations vs. Responses
• ?????????????? Question/actual response/recorded
  response
• ???????? Coding for analysis

69
?????????????
???????,???????????????????????? ?? ??
70
?????

• ?????????????????
• ____________
• ____________
• ____________
• ____________
• ____________

71
?????????????
??,????????,??????????????????????????????????????
????? ?? ??
72
?????

• ??,????????,??????????????????????????????????????
  ?
• ??? ?? ??? ?????
• ??? ?? ??? ?????
• ????? ?? ??? ?????
• ????? ?? ??? ?????
• ???? ?? ??? ?????

73
?????????????
??????,??,?,?????????? ?? ??
74
?????

• ?????????????????
• ?? ?? ???
• ?? ?? ???
• ?? ?? ???

75
?????????????
??????????????? ?? ??
76
?????
??????????????????????????? ?? ???
77
?????
??10??,??????????? ????? ?????? ?????? ??????
78
???????
????????????????? ? ? ??
79
???????
?????????? ? 12??? ? 25-35 ? 12-19 ? 35-45 ?
19-25 ? 45???
80
???????
???? ??? ? ? ? ?? ? ??? ??? ? ? ? ?? ?
??? ??? ? ? ? ?? ? ???
81
???????
??????????? ? ??? ? ???? ? ??? ? ???
? ??? ? ??? ? ????? ? ???
? ????? ? ????? ? ??? ? ?????
82
???????

• ???????? _________

83
???????

• (?????????????)
• ??????????????????????? ? ? ? ?? ? ???

84
???????

• (????????)
• ????????? ? ? ? ??

85
???????

• (????????)
• ??????????????,?????
• ?? ? ?

86
???????

• ????????????
• ? ? ? ?? ? ???

87
???????

• (????????)
• ??????45??????

88
THANK YOU
89
Extra Slides
90
Learning Objectives

• List objectives of questionnaire
• Describe advantages and disadvantages of
  questionnaire
• List steps in questionnaire design
• Describe different types of questions and when to
  use them
• Identify characteristics of effective
  questionnaire
• Define pilot testing
• Describe ways to avoid common problems
• Explain sensitive issues related to translating
  questionnaire

91
A Questionnaire is a Way to Measure

• It is a list of questions (answered by a
  respondent) to generate an indirect measure of
  the variables under investigation.
• Questions regarding
• - exposure - outcome -
  both
• Design and administration of a questionnaire is
  critical part of study.
• Poor design or administration can decrease the
  reliability and the validity of a measure.

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????? Types of Variables
?? Variable
???? Quantitative measurement
????? ?? Qualitative or categorical
???? (??????) (??,??) Continuous
(real-valued) e.g. height
????? (?????) Discrete (count data) e.g.
number of admissions
???? (?????? ???) Ordinal (ordered) e.g.
response to treatment
???? (???,???) Nominal (not ordered) e.g.
nationality
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Objectives of a questionnaire

• To ensure that the information obtained is as
  accurate and as relevant to the study as possible
• To maximize the proportion of subjects answering
  the questionnaire as high a response rate as
  possible

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