Quantitative research Quiz Answers

Transcription

1 Quantitative research Quiz Answers 1. What is a clinical trial? A. A clinical trial is an experiment where patients volunteer to test new ways of screening for, preventing, diagnosing or treating a disease. B. A clinical trial is a naturally occurring observational study where patients volunteer to be followed over time to look at preventing, diagnosing or treating a disease. A clinical trial differs from observational studies in that participants receive an intervention which is decided upon by the research staff. Therefore a trial is a planned experiment, rather than a study which collects observational data. Observational studies would be more likely to study the natural course of a disease or a participant s lifestyle choices and how they relate to the development of outcomes. 2. Randomisation is when: A. Each participant has an equal chance of being allocated to intervention or control B. Every other participant has an equal chance of being allocated to intervention or control The same procedure has to be followed for each participant in a trial to avoid bias. Therefore, each participant has to have an equal chance of being allocated to either group. If they do not have equal chances, then the two groups could become very different in their characteristics. 3. The major purpose of random assignment in a clinical trial is to: A. help ensure that study subjects are representative of the general population B. facilitate double-blinding C. facilitate measurement of outcome variables D. ensure that the study groups are comparable on baseline characteristics E. reduce selection bias in allocation of treatment Randomisation is important to ensure comparability of treated and untreated subjects. For example, factors such as age, sex, key exposures such as smoking, stage/severity of the condition, which could be related to the outcome of the trial need to be equally distributed between the randomised groups. Therefore, each participant needs to have an equal chance of being in either group. For example, if all patients with severe disease were put into the treatment group, they might have a worse outcome because they are more sick, and so the treatment may not seem to be better than no treatment, which may be the wrong conclusion.

2 4. Appropriate methods of randomisation include: Select all that apply. A. Throwing the dice B. Choosing every other person from a list C. Selecting all people born on the same day of the week D. Central computer generated randomisation tables s Randomisation has to be a process which is truly random and which ideally cannot be tampered with. There should be an equal chance of each patient being allocated to either group. 5. The purpose of concealing the allocation of the intervention in a trial is to: A. Ensure that nurses cannot choose their favourite patients to get therapy. B. Ensure that patient or observer do not know which therapy is being given during the study. C. Ensure that patients can t compare with each other if they get different therapy. Concealment allocation is important so that the queue of participants cannot be tampered with i.e. patients cannot be selected for inclusion into the study based on the knowledge of the whether the next participant will receive the intervention. For example, concealment of the allocation would not allow an investigator to manipulate the study by putting patients that he thinks would do well on the active treatment in a placebo controlled trial. Otherwise, this could lead to systematic differences between the groups, which would affect the outcome. 6. An advertisement in a medical journal stated that '2,000 subjects with sore throats were treated with our new medicine. Within 4 days 94% were asymptomatic'. The advertisement claims that the medicine was effective. Based on the evidence given above, the claim: A. is correct B. may be incorrect because the conclusion is not based on a rate C. may be incorrect because of failure to recognise a long-term cohort phenomenon D. may be incorrect because no test of statistical significance was used E. may be incorrect because no control or comparison group was involved In the above example, it is possible that if 2000 people with a sore throat were also treated with a dummy drug (placebo), 94% may have also become asymptomatic within 4 days, because that is the natural course of disease of the sore throat! Ideally, people with a sore throat would be randomised to receive either the medicine or a placebo / standard treatment, and the outcome of the percentage of

3 people with a resolved sore throat at 4 days compared. That is to say, to prove the effectiveness of this treatment, a control/comparison group is required. 7. The purpose of blinding in a study is to: A. achieve comparability of treated and untreated subjects B. reduce the effects of sampling variation C. avoid observer and subject bias D. avoid observer bias and sampling variation E. avoid subject bias and sampling variation Observer bias is a systematic difference between a true value and the value which is actually observed / recorded e.g. missing an abnormality (counting an outcome), or finding one where none in present. If the observer knows in which group the patient is in, they may be systematically more/less likely to observe the outcome. On the same lines, subject knowledge of the group they are in may affect their behaviour and consequently their outcomes in a certain way for example placebo patients may complain of more pain (knowing they are on placebo) and therefore make the active intervention group appear more effective. 8. Bias can be best defined as: A. Systematic (non-random) error arising from the design or conduct of a study B. A desirable quality that you want to include in your study design. A bias is an error which falls predominantly in one direction for example being more likely to give extra supportive interventions to a placebo group than an intervention group (performance bias), which could lead to a reduction in the effect size of the intervention. Biases can occur at all stages in the design and conduct of the study, and can easily affect the outcome measures and therefore the conclusions of the study, so they need to be eliminated. 9. Selection bias can best be described as leading to: A. Systematic similarities in participant characteristics at the start of a trial B. Systematic differences in participant characteristics at the start of a trial C. Similarities between the study population and the whole population eligible for the study Selection bias most commonly refers to what occurs when participants with certain characteristics are channelled into one group (i.e. the intervention or the control group) rather than the other. Therefore, the groups become different at baseline. This can bias the results and lead to a statistically significant difference between the groups at the end of the study, which is not a true effect of the intervention. Sometimes, selection bias is used to describe a situation where study participants are not representative of the eligible population from which the study sample was

4 taken. Examples include only including persons present at a particular place at a particular time in a survey, (i.e.a non-random sample), only including participants from one GP practice in the study, not including participants who cannot be contacted by . This may invalidate conclusions and generalisations of the study as the results only pertain to a select group of the population, and may not apply to everyone. 10. Performance bias refers to: A. How effective the therapy has been B. How well the researcher performed the study C. Participant expectations influencing their response to treatment Performance bias can occur both from the researcher and from the participant. If a participant knows they are in the intervention group, this can make them more positive about the results of the intervention, and this could make it appear more effective. Likewise, if a researcher knows that a participant is in the intervention group, they could be more likely to give extra support to make sure that the intervention works as well as they would wish it to. 11. Residents of 3 villages with 3 different types of water supply were asked to participate in a survey to identify cholera carriers. Because several cholera deaths had occurred in the recent past, virtually everyone present at the time was submitted to examination. The proportion of residents in each village who were carriers was computed and compared. Classify this study. A. Cross-sectional study B. Case-control study C. Cohort study D. Experimental study (clinical trial) The aim of this study is to estimate how many of the inhabitants in villages known to be at risk from cholera were carriers of cholera. A sample of the whole population was selected, and everyone was assessed to see whether they had cholera or not i.e. the measurement of a certain characteristic was performed for everyone. Then, the proportion of those who were carriers over the total population was calculated. This is an example of a cross-sectional study, where a certain characteristic is measured for everyone in a sample of a population, and a proportion (or percentage) is calculated as the main study outcome. 12. In a small pilot study 12 women with endometrial cancer (cancer of the uterus) and 12 women with no apparent disease were contacted and asked whether they had ever used estrogen. Each woman with cancer was matched by age, race, weight and parity to a woman without disease. What kind of study design is this? A. Cohort B. Case-control

5 C. Cross-sectional The participants for this study were selected on the basis of whether they had the disease of interest (endometrial cancer) or not. These are the cases. Then, they were matched to women with no disease based on certain characteristics which are related to the risk of having endometrial cancer. These women are the controls, as they have no disease, and so the study is termed case-control. 13. In order to assess the relationship between recurrent otitis media and the presence of a pet in the home, a paediatrician reviewed the medical charts of patients in the age group 2 to 5 years in her large practice. She identified 50 children who had experienced 3 or more otitis media infections during the past year, and 50 who never experienced such infections. In parental interviews she found that there were pets in the homes of 30 of the children with otitis media and in 20 of the homes in which there was no otitis media. What type of study is this? A. Series of case reports B. Case-control C. Cohort The participants for this study were selected on the basis of whether they were cases of a disease of interest. The definition of a case (the case definition ) here is children aged 2 to 5 years with 3 or more otitis media infections during the past year. She compared the frequency of the exposure (pets) in her cases with a control group (no otitis media infections). So this is a case-control study. 14. In 1990 a study was implemented to evaluate the relationship between lung cancer and pulmonary tuberculosis. 5,000 patients aged were identified who had been successfully treated for pulmonary tuberculosis (TB) between 1935 and 1942, as were 5,000 who were never diagnosed with TB. National death certificates were searched to identify the cause of death in these patients in the intervening years. Death from lung cancer was ascertained in 10 of the TB survivors and in 7 of those never known to have TB. What type of study is this? A. Series of case reports B. Case control C. Cohort The participants in this study were selected on the basis of an exposure i.e. whether or not they had been successfully treated for TB. Their records were then searched for the outcome of death from lung cancer. The fact that this study was done using previously collected data makes it a retrospective cohort study, which would be the least expensive and time-consuming way of answering this particular research question.

6 15. In order to compare prosthetic devices, eligible patients undergoing elective hip replacement were randomly assigned to receive one or the other device. The patients were followed from the time of the replacement. Device failures requiring surgical intervention were recorded. There were 10 failures seen in patients receiving Device 1 during 500 person-years of follow-up and 20 failures in 5,000 person-years of follow-up for those receiving Device 2. What type of study is this? A. Series of case reports B. Case-control C. Cohort This study is a direct comparison of 2 prosthetic devices. The devices were assigned to patients through randomisation, which indicates that it is an experimental trial, rather than an observational study of device use in normal practice. The outcome is the failure rate, which was measured after a certain period of follow-up, also indicating that the study is prospective and measurements were pre-defined.