ARA0103 Aferafri Rannskna

1
ARA0103 Aðferðafræði Rannsókna
Australian Medical Sheepskin

• Fyrirlestrar 7 og 8
• Experimental design I/Tilraunasnið I

quantitative/megindlegur
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What is the problem?Hvað er vandamálið?
fyrst skref í rannsókn
Dæmi...

• Long term patients with bedsores.Langtímasjúkling
  ar með legusár.

3
What are the variables?Hverjar eru breyturnar?

• Independent variablesÓháðar breytur
• Bed mattress in use./Rumdýna í notkun
• Frequency of patient turning.
• Time in hospital.
• Dependent variablesHáðar breytur
• Number of pressure ulcers./Fjöldi legusára
• Patient comfort.
• Using a sheepskin mattress cover might make the
  patient too hot.

Athugasemd in student projects, start by
considering only one independent variable and one
dependent variable.
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What is the intervention?Hvað er inngrip?

• Medical Sheepskin
• http//www.healingfibres.com/
• http//www.medicalsheepskins.com/index.html
• http//www.classicsheepskin.com/medical.htm
• 2x frequency of patient turning/tvöfalda tíðni
• Education/Menntun...
• If you can move yourself, change position every
  15 minutes.
• Eat properly/Borða rétt
• ...
• Use pressure relieving supports...

olnbogi
ökkli
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Að bera saman gögn...

• Applying an intervention may be unnecessary if
  you can compare data from different
  wards/deildir, hospitals/sjúkrahús or nursing
  homes/hjúkrunarheimili.

gögn hér
gögn hér
gögn hér
More turning of patients?
Less turning of patients?
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State the null hypothesis H0Tilgreina
núlltilgátuna H0- áhrif er ekki til -
dæmi

• A sheepskin mattress cover has no effect on the
  number of bed sores.
• Doubling frequency of patient turning has no
  effect on the number of bed sores.
• Educating patients on how to prevent bed sores
  has no effect on the number of bed sores.

Usually endeavour to reject the null
hypothesis.Yfirleitt er leitast við að hafna
núlltilgátuna.
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State the alternative hypothesis HaTilgreina hin
tilgátuna H0- áhrif er til -
dæmi

• A sheepskin mattress cover reduces the number of
  bed sores.
• Doubling frequency of patient turning reduces the
  number of bed sores.
• Educating patients on how to prevent bed sores
  reduces the number of bed sores.

...minnkar fjöldi legusára
Ef þú ert að nota t-próf, til dæmis, vonin er að
segja núlltilgátan er ekki rétt, frekar hin
tilgátan hlýtur að vera rétt.
hin tilgátan aðaltilgátan
8
Select measurement toolsVelja mælitæknar

• Hjúkrunarfræðingur getur lagt saman legusár
  beint.
• Rannsóknarmaður getur lagt saman legusár að nota
  myndir sjúklings.
• Hjúkrunarfræðingur getur mælt hita sjúklings.
• A questionnaire can be used to assess patient bed
  comfort.
• rannsóknarmaður má skrifa sjálf
• eða nota/breyta spurningalista sem er til hjá
  t.d. http//www.medalreg.com/,

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ValidityRéttmæti
mælitæknar

• Measurement tools are reliable if you get the
  same answer by repeating the measurement.
• A nurse might fail to count a Stage I bed sore on
  one ankle which was counted by another nurse.
• Procedures have to be followed to measure blood
  pressure reliably.
• Measurement tools are valid if they measure what
  you want them to measure.
• On a questionnaire, patients may say they are too
  hot, but their temperatures measured using
  thermometers suggest they were not too hot.
• Maybe they completed the questionnaires on a very
  hot sunny day?

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Is the intervention potent?Er inngrip sterkur?

• A sheepskin mattress cover that is too thin might
  not work.
• A video showing someone die in the final stages
  of smoking-related lung cancer is a more potent
  intervention than an information
  leaflet/bæklingur.
• Toe-grasp training for 30 seconds every month is
  unlikely to improve balance.

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Pilot study/Forathugun,Forrannsókn

• If possible, conduct a pilot study with a small
  number of people beforehand (4-6).
• Pilot subjects should be similar to the subjects
  in the actual experiment.
• Pilot studies check on
• Wording of questionnaires/Orðalag spurningalista.
• How often are patients turned?
• Aldrei Stundum Oft Mjög Oft
• Hvað þýðir stundum, oft, og mjög oft?
• Unclear instructions/Óvissar leiðbeiningar.
• How often should the sheepskin mattress cover be
  washed?

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Use a control groupNota samanburðarhóp
confounding variable/truflandi breyta

• The control group do not receive the
  intervention.
• From an ethical point of view, the control group
  should receive normal treatment/venuleg meðferð.
• Using a control group is the only way to deal
  with confounding variables.
• age, sex, weight, surgery, mobility (gangandi?),
  ...
• Patient characteristics in the control group
  should be similar to the intervention group.
• Gengur ekki að bera saman 20-25 ára með 70-75
  ára...

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Randomized Controlled Trial hrein
tilraun slembi-íhlutunarrannsókn
eligibility criterion/úrtaksskilgreining
Identify eligible subjects
Obtain informed consent/Afla upplýsts samþykkis
overview/yfirlit
Þátttakendur
Non-participants
Willing
Unwilling
How many unwilling?
Randomization/Tilviljunarval
between subjects/ milli hópa
Intervention group (I)
Control group (C)
Participants
Drop outs
Þátttakendur
Brottföll
Data collection
Data collection
Safna gögn
Safna gögn
Number of bed sores
Number of bed sores
How many drop outs?
How many drop outs?
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Randomization/Tilviljunarval

• Ideally, a third party allocates subjects to the
  control (C) or intervention (I).
• Called allocation concealment/Kallað leynd
  úthlutunar.
• Avoids experimenter bias/Forðast áhrif
  tilraunamanns
• An experimenter could allocate younger patients
  to the sheepskin group (I).
• An experimenter could allocate only
  post-operative patients to the control group (C).
• Subjects can be given a number and numbers can be
  selected at random using a computer program.

http//www.graphpad.com/quickcalcs/randomize1.cfm
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Randomized Controlled Trial (RCT)
overlap/skörun
Inngrip
Samanburðahópur
Inngrip
tíðni
tíðni
Samanburðahópur
-gt fjöldi legusára
-gt fjöldi legusára

• Obvious that the intervention reduces the number
  of leg sores. A t-test is not needed.
• Auglóst að inngrip minnkar fjöldi legusára.
  t-próf er óþarft.

• A t-test is needed. Is p lt 0,05? If so, the
  difference is statistically significant and the
  intervention reduces the number of leg sores.
• t-próf er þarft. Er p-gildi lt 0,05? Ef svo,
  mismunurinn er tölfrælega marktæk og inngrip
  minnkar fjöldi legusára

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Within subjects design/Innanhópasnið
sample size/úrtaksstærð
úrtaksstærð n1

• Single subject/einn þátttakandi

AB design/AB snið. Leggja saman legusár. Fyrr
(A) og á eftir (B). Ekki hægt að nota
tölfræðipróf, svo er ekki hægt að álykta um
þýði. Líka ABAB, ABABAB snið.
A
B

• An individual patient may be so unique and in
  need of such help, that only they receive the
  intervention.

Dr House...
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Within subjects design/ Innanhópasniðimbalanced/ó
jafnvægt
n10
paired or related or dependent data -gt nota
parað t-próf
safna gögn lok mars og lok apríl
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What if ?/Hvað ef?

• During the control period in March, there are
  nursing staff shortages and patients are turned
  only 50 of the time.
• This would effect the measurements of bed sores
  at the end of the control period. (skekkja)
• This within subjects design is said to be
  imbalanced and is fatally flawed.
• gengur ekki að nota slíkt snið

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Within subjects design/ Innanhópasniðbalanced/í
jafnvægi
cross-over
n10
safna gögn lok mars og lok apríl
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Within subjects design/Innanhópasnið
advantage/kostur

• By using the same subjects, there is better
  control of variability between subjects.
• But sometimes it is impossible for subjects to
  receive both the control and the intervention.
• Post-operative patients can be measured only
  once. They are no longer post-operative after
  receiving either the control or the intervention.

post-operative/eftiraðgerðar-
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Within subjects design/Innanhópasnið

• Sometimes the cross-over design leads to ethical
  problems.
• If the intervention works really well for an
  individual patient, should they be taken of the
  intervention and put on the control ?
• Gengur ekki að hætta að lækna að nota inngrip!
• Patients are no longer blinded.Sjúklingar eru
  ekki lengur blindir.
• They can realise that the use of the sheepskin
  matress cover is the intervention.

siðfræðilegt vandamál
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Within subjects design/Innanhópasnið
ójafnvægt

• Sometimes the cross-over itself is imbalanced.
• Going from a sheepskin to a normal mattress is
  not the same as going from a normal mattress to a
  sheepskin.
• Sometimes a patients health status can change
  over time.
• Becoming post-operative as you are about to
  cross-over between control (C) and interventiion
  (I).
• Data for such patients may have to be left out.
• Data cleansing/Gagnahreinsun
• Deletion or drop-out/Brottfall

heilsuástand breytast yfir tíma...
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Between subjects design/Millihópasnið.
Dæmi Regarding diastolic blood pressure, is
there a statitiscally significant difference
between men and women?Varðandi blóðþrýsting, er
tölfræðilega marktækur munur til á milla manna og
kvenna? Men 76, 76, 74, 70, 80, 68, 90,
70, 76, 80, 68, 72, 96, 80, 90, 72 Women 76, 70,
82, 90, 68, 60, 62, 60, 62, 72, 68, 80,
74 Perform an independent t-test (2-tailed,
unequal variances).Reiknaðu óparað/óháð t-próf
(tvíhliða, ójafnar dreifingar). What is the
significance level? __________ (hvað er
marktektarstig?) What is the effect size?
__________ (hver er stærð áhrifa?)
The null hypothesis/Nulltilgátan There is no
difference in diastolic blood pressure between
men and women.Munur á blóðþrýstingi er ekki
til á milli manna og kvenna.
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Equal sample sizes is better.Jafnar úrtakstærðir
er betri.
The value of p needs to be less than 0,05 for
statistical significance. p-gildi lt 0,05 þýðir að
munur er tölfræðilega marktækur.
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more subjects? fjölga þátttakendum?
power of a statistical test/styrkur tölfræðiprófs

• p gildi er ekki minna en 0,05 en er lítið (0,07).
• Munur á milli meðaltala er 6.
• If there were more subjects, it might be possible
  to detect a real difference.
• A negative result in a statistical test might be
  because you do not have enough subjects. The
  statistical test might not have enough
  statistical power to detect the difference
  between means.
• What if we have another set of measurements of
  diastolic blood pressure that are similar to the
  first?
• Is it possible to obtain statistical
  significance?Er hægt að ná tölfræðileg marktekt?

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How many subjects?Hve margir þátttakendur?
power of a statistical test/styrkur tölfræðiprófs

• Ef þú ert að reikna út meðaltal og staðalfrávik,
  úrtaksstærð n hlytur að vera gt10. (segir Andy)
• ngt20 er betri
• ngt30 er ennþá betri.
• The greater the number of subjects the greater
  the statistical power.

ngt30 meiri styrkur
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Dæmi
afköst
fjöldi í hverju hólfi sniðsins

• Ef n 10, líkur á því að finna mun (sem er til)
  er 0,3.
• Ef n 20, líkur á því að finna mun (sem er til)
  er 0,6.

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Standard error of the meanStaðalvilla meðaltala

• The standard deviation of the sampling
  distribution of the sample mean is called the
  standard error of the mean.Staðalfrávik
  úrtakadreifingar úrtaksmeðaltals kallast
  staðalvilla meðaltal.

The standard error of the mean gets less with a
bigger sample. Staðalvilla meðaltala minnkar með
stærra úrtaki.
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RVLS Sampling Distributions
normaldreifing
s5,00 þýðisstaðalfrávik
n5
S2,27 staðalfrávik úrtakadreifingar
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RVLS Sampling Distributions
normaldreifing
s5,00 þýðisstaðalfrávik
n10
S1,54 staðalfrávik úrtakadreifingar
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RVLS Sampling Distributions
normaldreifing
s5,00 þýðisstaðalfrávik
n25
S1,02 staðalfrávik úrtakadreifingar
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Central Limit Theorem/Markgildissetningin
skewed/skekkt
non-parametric test/stikalaust próf
parametric test/stikapróf
n25

• Even if the population distribution is skewed,
  the sampling distribution of means is normal if
  the sample size n is large enough.
• If the population distribution is skewed and the
  sample size is small, you must use non-parametric
  statistics. These tests have less statistical
  power. The equivalent of the parametric
  independent t-test is called the Mann-Whitney U
  test.

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Diabetes/Sykursýki
http//dtc.ucsf.edu/ Diabetes Teaching Center
Within subjects design/ Innanhópasnið
Dæmi Does diabetes education improve scores on
tests about diabetes knowledge?
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
paired or related or dependent t-test/parað t-próf
Perform a paried/related/dependent t-test
(2-tailed).Reiknaðu parað t-próf
(tvíhliða). What is the significance level?
__________ (hvað er marktektarstig?) What is the
effect size? __________ (hver er
stærð áhrifa?)
Null hypothesis/Nulltilgátan There is no
difference in scores after a course about
diabetes. Munur á stigafjölda er ekki til eftir
nám um sykursýki
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p-gildi/marktektarstig er minna en 0,05. Við
höfum tölfræðileg marktekt.
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A two-tailed or one-tailed t-test?Einhliða próf
eða tvíhliða próf?

• Diabetes education will not decrease peoples
  knowledge about diabetes.
• Í nám, þú lærir eitthvað...
• We can use the one-tailed t-test result.
• The value of p is 0,00248.
• statistically significant/tölfræðilega marktæk

t-3,69
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Clinically significant effect?Klínísk marktæk
áhrif?

• The paired t-test result (one-sided) showed that
  diabetes education improves knowledge about
  diabetes.
• En áhrifastærð er aðeins 3,2.
• Er það klínísk marktæk?
• Do patients control their blood sugar levels
  better as a result of only slightly improved
  knowledge ?

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Statistical significance does not imply clinical
significance

• Reducing the mean number of bed sores by 1,0
  means one less bed sore for every patient.
• Að meðaltali og er klínísk marktæk
• Reducing the mean number of bed sores by 0,1
  means one less bed sore every 10 patients.
• Reducing the mean number of bed sores by 0,01
  means one less bed sore every 100 patients.
• Reducing the mean number of bed sores by 0,001
  means one less bed sore every 1000 patients.
• áhrifastærð er ekki klínísk marktæk

tölfræðilega marktæk er ekki sama sem klínísk
marktæk