from analysis plan to data collection

Helen Maguire

acknowledgements

Katharina Alpers, Yvan Hutin

its logical: data collection follows the analysis plan ..

Research question:? Risk factors for leptospirosis

Study objectives:Estimate association between water exposure and disease

Design/ indicator:Case controlOdds ratio

Analysis plan:Dummy table

Data elementsNeeded:? Water exposure? Sick

Data collection:Interview

Individual items:? Swam in water ? Sick

Consolidationof theinstrument

data quality

• reliability

• accuracy

Data quality

data quality

• reliability– reproducibility/repeatability/precision

– ability of a measurement to give the same result or similar result with repeated measurements of the same thing

– refers to stability or consistency of information

• accuracy• ability of a measurement to be correct on the

average

Data quality

reliability and accuracy

Data quality

ReliableAccurate

Not reliableAccurate

ReliableNot accurate

Not reliableNot accurate

reliability and accuracy

Data quality

some essentials

1. question-by-question guide

2. train staff who collect data

3. standardize the data collection procedure

4. control instruments or specimen collection

5. validate

Data collection

1 question by question guide(q-by-q)

• short document

• each question/data item – item by item

• guidance as to how the data should be collected

• derived variables explained

Data collection

2 train field workers

• select good, experienced field workers

• walk through q-by-q guide

• explain where data is

• clarify how to record it

• simulate interviews with team

Data collection

3 standardize data collection

• interviewers– work in teams

– resolve issues in the whole group

• instruments/specimens/samples– calibration, standardization, packaging, media,

transport

Data collection

4 control instruments

• team checks instrument/samples before leaving

• all take responsibility for the instrument:– names and signatures

• investigator checks instruments/samples as they come

Data collection

5 validate

how would you validate/verify?

example - triangulation to estimate the proportion of blood units screened for HIV

(internal validation)

• interview laboratory manager• ? what is the number of units screened

• observe practices of the laboratory technician– structured observation guide

• ? proportion of units tested

• review of registers - ? a sample– proforma

• ? number of tests ordered, performed

Instruments

data might include

• facts– individual characteristics

• height, age, income

– environment

• housing, family size

– behaviours, practices

• alcohol or tobacco consumption

• judgements – attitudes/opinions

• indicators of socio-economic status …

• blood test results

• environmental samples Instruments

list some ways to collect data

Instruments

• proformas– clinical records

– surveillance records

– registers

• questionnaires

• sampling /laboratory results

• other data – socio-economic status derived from postcode –via

linkages

– denominator data

– reference data

checking the instrument(s) against the analysis plan

• make sure you can collect what you need for each variable /indicator

• suppress unnecessary data collection or questions at interview– those that do not be used in the analysis

Production of the instrument

is a questionnaire good?why?

• list 5 advantages and 5 disadvantages

advantages of questionnaires

• can reach a large number of people

• relatively easy and economic

• relate directly to study question

• provide quantifiable answers

• relatively easy to analyse

possible disadvantage of questionnaire

• bias …?

• how might it be introduced at this stage?

• how would you avoid it?

• pilot - check for leading questions

how to reduce bias

• structured questionnaire

• ensure high response rate

• random choice of interview partners (next birthday)

• train interviewers

disadvantages of questionnaires• provide only limited insight into a

problem– the range of possible responses is limited – the question maybe misleading

Unclear question can lead to • misunderstanding • misinterpretation

• do not allow for mistakes– must be right from the beginning – missing data hard to chase

how to avoid ?

pilot testing of the questionnaire

• check that the questionnaire is:– clear

– understandable

– acceptable

• check flow and skip pattern

• check coding

• estimate time needed

Production of the instrument

how would you administer a questionnaire?

questionnaires

• internet/email/post self completion

• interviewer-administered– face to face

– telephone

what makes a well designed questionnaire?

what makes a well designed questionnaire?

• good appearance (easy for the eye)

• short and simple

• numbering / flow /sign-posting

/instructions/where to return and how

• relevant and logical

introduction

• covering letter/ interview introduction– Who are you / you work for

– Why are you investigating

– Where did you obtain the respondent’s name

– How and where can you be contacted

– Guarantee of confidentiality

– Length of interview (be honest)

⇒ Usefulness of study should be clear to all respondents

• Good morning ,

My name is Katharina Alpers .... , I work for ……..

You may have been already informed that a survey on risk

factors for being stung by a jellyfish will be done this week in

Mahon. This study has been approved by the Spanish national

ethical committee. Only anonymous data will be analysed. You

have been randomly selected to participate in this study. Your

participation is voluntary. The interview is about 10 minutes

long. Are you able to help us?

thanks so much .....

questions

do you like to go swimming and do you mind being

stung by jellyfish?

Yes No

what is the jellyfish situation? Good Bad

versus

how often did you see jellyfish during the last week?

Once Twice Three times or more Never Don´t know

did you see more than an average of 33 jellyfish/m2 salt water surface on more than 3 occasions that you went swimming in the morning last week?

Yes No

versus

have you seen jellyfish on more than 3 mornings last week?

Yes No Don´t know

main question formats

• closed format forced choiceYes Always No Sometimes Don’t know Never

• open format free textWhat did you do to avoid being stung by jellyfish? Please describe : __________________________________________________________________________________

• when would open questions be good ?

• what problems might there be with open questions?

advantages of open questions

• exploration possible – to generate hypotheses

• useful for exploring knowledge and attitudes• qualitative research

• focus groups

• trawling questionnaires

disadvantages of open questions

• interviewer bias

• time-consuming

• coding problems

• difficult to analyse

• difficult to compare groups

advantages of closed questions

• simple

• less discrimination against less verbally expressive people

• easy to code, record, analyse

• easy to compare

disadvantages of closed questions

• restricted number of possible answers

• possible loss of additional information

Compromise

if yes specify : __________”

which of the following beaches have you visited during your stay in Menorca?

Lazareto beach Yes No Don´t know

Cala’n Porter Yes No Don´t know Rafalet

Yes No Don´t know

Macarella Yes No Don´t

know

Sa Mesquida Yes No Don´t know

checklist

rating scale

how often did you see jellyfish during the past week?

Always Sometimes Seldom Never

Mornings

Lunchtime

Evenings

rating scalenumericalhow severe was your pain after you were stung?

(please circle) 1 2 3 4 5 6 7

Not painful at all Very painful

analoguehow severe is your pain (put the tick on the line)

0 10

Likert ScaleRensis Likert, 1903-1981Five (or more) ordered response levels

Jellyfish also have the right to swim in the Mediterranean sea

I strongly disagree

I disagree

I neither agree or disagree

I agree

I strongly agree

problems and pitfalls

• avoid questions that ask two things at once - you won’t know which part people are answering:

have you seen or been stung by jellyfish?

• ambiguity.....

do you swim a lot?

problems and pitfalls• avoid jargon/abbreviations/slang

should jellyfish sting victims receive PEP?

(post exposure prophylaxis)

• avoid not mutually exclusive options

What is your age ? 16-20 20-25 25-30 35-40

summary

a well designed questionnaire:

• helps you answer your research question

• minimises potential sources of bias

-> increases the validity of the replies

• is more likely be completed

questionnaire validation

• use or adapt existing questionnaires – validated

• new questionnaires– need to be tested (pilot)

conclusion

• don’t forget to thank the interviewed persons

• tell them when the results will be available and where

take home messages

• think instruments, data sources, not only questionnaire

• list your indicators

• prepare your variables ->indicators

• prepare dummy tables

• polish, polish and polish to ensure good data quality

• thanks for your attention