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 control Odds ratio Analysis plan: Dummy table Data elements Needed: ? Water exposure ? Sick Data collection: Interview Individual items: ? Swam in water ? Sick Consolidation of the instrument

• • reliability accuracy

data quality

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

reliability and accuracy

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Reliable

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Accurate

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Reliable

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Not accurate

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Not reliable



Accurate



Not reliable



Not accurate

Data quality

some essentials

1.

2.

3.

4.

5.

question-by-question guide train staff who collect data standardize the data collection procedure control instruments or specimen collection 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/m surface on more than 3 occasions that you went swimming in the morning last week?   Yes No 2 salt water versus have you seen jellyfish on more than 3 mornings last week?

   Yes No Don´t know

main question formats

• closed format  Yes No Don’t know    forced choice Always  Sometimes Never   • open format  free text What 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 : __________”

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

Lazareto beach  Yes Cala’n Porter Rafalet  Yes  Yes    No  No  No  Don´t know Don´t know Don´t know Macarella  Yes  No  Don´t know Sa Mesquida  Yes  No  Don´t know

rating scale how often did you see jellyfish during the past week?

Always Sometimes Seldom Never Mornings Lunchtime         Evenings    

rating scale numerical how severe was your pain after you were stung? (please circle) 1 2 3 4 5 6 7 Not painful at all Very painful analogue how severe is your pain (put the tick on the line) 0 10

Likert Scale Rensis Likert, 1903-1981 Five (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 which part people are answering: - you won’t know have you seen or been stung by jellyfish?

• ambiguity .....

d o 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