ARA0103 Aðferðafræði Rannsókna

1. ARA0103 Aðferðafræði Rannsókna Australian Medical Sheepskin Fyrirlestrar 7 og 8 Experimental design I/Tilraunasnið I quantitative/megindlegur Dr Andy Brooks

2. Dæmi... Hvað er vandamálið? • Langtímasjúklingar með legusár. • bed sores/pressure ulcers Dr Andy Brooks

3. What are the variables?Hvað eru breyturnar? • Independent variables/óháðar breytur: • Support mattress in use. • Frequency of patient turning. • Time in hospital. • Dependent variables/háðar breytur: • Number of pressure ulcers. • Patient comfort. • Using a sheepskin mattress cover might make patient too hot. Athugasemd: in student projects, start by considering only one independent variable and one dependent variable. Dr Andy Brooks

4. What is the intervention/inngrip? • Medical Sheepskin… • http://www.healingfibres.com/ • http://www.medicalsheepskins.com/index.html • http://www.classicsheepskin.com/medical.htm • 2x frequency/tíðni of patient turning... • Menntun... • If you can move yourself, change position every 15 minutes. • Eat properly/Borða rétt • ... • Use pressure relieving supports... olnbogi ökkli Dr Andy Brooks

5. 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? Dr Andy Brooks

6. 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. Yfirleitt er leitast við að hafna núlltilgátuna. Dr Andy Brooks

7. 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. 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 Dr Andy Brooks

8. Select measurement toolsVelja mælitæknar • Hjúkrunarkona getur lagt saman legusár beint. • Rannsóknarmaður getur lagt saman legusár að nota myndir sjúklings. • Hjúkrunarkona getur mælt hita sjúklings. • A questionnaire/spurningalisti can be used to assess patient bed comfort. • Rannsóknarmaður má skrifa sjálfur • eða nota/breyta spurningalista hjá http://www.medalreg.com/, … Dr Andy Brooks

9. mælitæknar Reliability and ValidityÁreiðanleiki og Réttmæti • 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/aðferðir have to be followed to measure blood pressure. • 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? Dr Andy Brooks

10. 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. Dr Andy Brooks

11. Pilot study/Forathugun,Forrannsókn • If possible, conduct a pilot experiment 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 þýða stundum, oft, og mjög oft? • Unclear instructions/óvissar leiðbeiningar . • How often should the sheepskin mattress cover be washed? Dr Andy Brooks

12. confounding variable/truflandi breyta Use a control groupNota samanburðarhóp • 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, ... • Patient characteristics in the control group should be similar to the intervention group. • Gengur ekki að bera saman 20-25 ár með 70-75 ár... Dr Andy Brooks

13. Randomized Controlled Trial hrein tilraun eligibility criterion/úrtaksskilgreining Identify eligible subjects overview/yfirlit Obtain informed consent/Fá upplýst samþykki 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? Dr Andy Brooks

14. Randomization/Tilviljunarval • Ideally, a third party allocates subjects to the control (C) or intervention (I). • This is called allocation concealment. • Eliminates experimenter bias/skekkja. • 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 random numbers can be selected from a table of random numbers or using a software tool. http://www.graphpad.com/quickcalcs/randomize1.cfm Dr Andy Brooks

15. Dr Andy Brooks

16. Randomized Controlled Trial (RCT) I C At some point we begin to believe there is a real difference between the two distributions – mismunurinn er til ( t-próf, p-gildi minna en 0,01). “Sheepskin mattress covers reduce the number of bed sores on average.” Dr Andy Brooks

17. sample size/úrtaksstærð Within subjects design/innanhópasnið • Single subject/einn þátttakandi úrtaksstærð n=1 AB design/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... Dr Andy Brooks

18. Within subjects design/ innanhópasniðimbalanced/ójafnvægt n=10 paired or related or dependent data -> nota háð t-próf safna gögn lok mars og lok apríl

19. What if ?/Hvað ef? • During the control period, 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 Dr Andy Brooks

20. cross-over Within subjects design/ innanhópasniðbalanced/í jafnvægi n=10 safna gögn lok mars og lok apríl

21. Within subjects design/ innanhópasnið • By using the same subjects, there is better control of variability between subjects. • 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- Dr Andy Brooks

22. 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 ? • Patients are no longer blinded. • They can realise that the use of the sheepskin matress cover is the intervention. • Sometimes the cross-over itself is imbalanced. • Going from a sheepskin to a normal mattress might not be the same as going from a normal mattress to a sheepskin. • Sometimes a patient´s 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. (brottfall) Dr Andy Brooks

23. Between subjects design/Millihópasnið. Dæmi Does the diastolic blood pressure between men and women differ? 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 Calculate the results of an independent t-test. (2-tailed, unequal variances) What significant level is reached? __________ (marktektarstig) What is the size of the effect? __________ (stærð áhrifa) Null hypothesis/Nulltilgátan: “There is no difference in diastolic blood pressure between men and women.” Dr Andy Brooks

24. It is better to have equal sample sizes. The value of p needs to be less than 0,05 for statistical significance. The smaller p is, the greater the statistical significance. Dr Andy Brooks

25. power of a statistical test/styrkur tölfræðiprófs More subjects? • p gildi er ekki minna en 0,05 en er lítið (0,07). • The difference between means is 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 statisticalpower 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 Dr Andy Brooks

26. power of a statistical test/styrkur tölfræðiprófs How many subjects? • Ef þú ert að reikna út meðaltal og staðalfrávik, úrtaksstærðin hlytur að vera >=10. • n>=20 is better • n>=30 is even better. • The greater the number of subjects the greater the statistical power. Dr Andy Brooks

27. Standard error of the mean/Staðalvilla • The standard deviation of the sampling distribution of sample means is called the standard error of the mean. • As n increases, the standard error of the mean decreases. Dr Andy Brooks

28. RVLS Sampling Distributions σ=5,00 S=2,27 n=5 Dr Andy Brooks

29. RVLS Sampling Distributions σ=5,00 S=1,54 n=10 Dr Andy Brooks

30. RVLS Sampling Distributions σ=5,00 n=25 S=1,02 Dr Andy Brooks

31. skewed/skekkt Central Limit Theorem/Markgildissetningin • 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, experimenters 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. parametric test/ stikapróf non-parametric test/ stikalaust próf n=25 Dr Andy Brooks

32. Diabetes/Sykursýki Within subjects design/ Innanhópasnið Dæmi Does diabetes education improve scores on tests about diabetes knowledge? S1 paired or related or dependent t-test/háð t-próf Calculate the results of a dependent t-test. (2-tailed) What significant level is reached? __________ (marktektarstig) What is the size of the effect? __________ (stærð áhrifa) Null hypothesis/Nulltilgátan: “There is no difference in knowledge scores after receiving diabetes education.” Dr Andy Brooks

33. p gildi/marktektarstig er minn en 0,05. Við erum með tölfræðileg marktekt. Dr Andy Brooks

34. A two-tailed or one-tailed t-test?Einhliða próf eða tvíhliða próf? • Diabetes education will not decrease peoples’ knowledge about diabetes. • We can use the one-tailed t-test result. • The value of p is 0,00248. • statistically significant/tölfræðilega marktæk t=-3,69 Dr Andy Brooks

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

36. 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. • stærð áhrifa er ekki klínísk marktæk tölfræðilega marktæk er ekki sama sem klínísk marktæk Dr Andy Brooks