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Design of Clinical Trials in Radiology for
Improved Assessment of Diagnostic Tests.

Stavroula J. Theodorou, M.D., Daphne J. Theodorou,
M.D. Department of Radiology; University of
California, San Diego, Veterans Affairs Medical
Center, San Diego, CA

ABSTRACT

Proper design of clinical trials has become a prerequisite for

both the performance and interpretation of research in

radiology as well as in other disciplines in medicine. This paper

reviews the process of designing clinical research, the research

question, the review of existing data, the study design, the

study population, and the study measurements. Theodorou SJ,

Theodorou DJ. Design of clinical trials in radiology for improved

assessment of diagnostic tests. Internet Medical Journal, 2005, 5:1.

http://www.medjournal.com/forum/showthread.php?p=1450




                                    1
In recent years, several studies have demonstrated the

inadequate level of knowledge and understanding of study design and

statistics held by physicians including radiologists (Weiss and Samet,

1980, Berwick et al, 1981, Goldin and Sayre, 1996). Rigorous

research begins with the precise definition of the research question,

which describes the uncertainty of something observed in the

population that the researcher believes can be resolved by making

measurements on study subjects (Hulley and Cummings, 1988).



THE RESEARCH PROTOCOL

The research protocol is the written plan of the investigation that

defines the research question, the rationale for the study, the

materials and methods to be used in detail, and the anticipated

problems that may occur in the execution of the study. Optimally, the

steps taken to avoid bias and thus, eliminate the most common reason

responsible for the lack of validity should also be described in detail in

the study protocol. Ideally, the protocol is evolving and improving

during the execution of the study, as the researcher reevaluates and

revises its components. A timeline of the expected dates of

completion of each part of the study and factors which warrant the

feasibility of the study, including financial and other logistical

constraints encountered in the research process, should be precisely



                                      2
stated in the protocol, as well. Indeed, research funding is one of the

major parameters that ensures the feasibility of the research study. In

fact, a rigorous and detailed protocol should always be a prerequisite

for all clinical trials and in terms of academic honesty, should never

aim at the request of research funds, alone.



THE RESEARCH QUESTION

The research question is developed in a form termed the hypothesis.

Hypothesis defines the study design, the sample, and the

measurements that need to be made. Good research questions should

qualify the following criteria: I) importance, II) novelty, III) feasibility

to answer, IV) ethics, and V) relevance. The following research

question serves as an example for illustrative purposes. Suppose a

new imaging modality (IM) has been developed that provides the

radiologist with data concerning the disease (D). The research

question inquires whether IM provides information associated with the

diagnosis of D. IM would be of any significant value and the research

question would prove a good one, if only D is a major health problem

resulting in great morbidity, if left undiagnosed. If the diagnosis of D

can already be made utilizing other existing imaging modalities or

even can be attained on the basis of clinical and/or laboratory findings,

then the research question would be of a limited importance.



                                      3
Traditionally, this question of importance is also known as the

“so what? ” criterion, in terms of why someone should spend his time

and money to answer it. With respect to the answer to the research

question itself, ideally it has to be novel, so that it can provide

additional information to the already existing scientific knowledge or

optimally constitute new information. Given the necessity of a

thorough investigation of previous studies associated with the present

research question, a review of the literature is considered extremely

important. However, this certain procedure may lead to the

modification of the initial research question, since questions which

remain unanswered may be identified.

      For the purposes of the study, one of the main features of the

research question is the answerability, as the research question should

be stating the study’s major clinical variables and also be explicit. In

the aforementioned example however, the research question is rather

vague and as a result it remains unanswerable, necessitating a

modification. Indeed, questioning whether IM is sensitive and specific

for the diagnosis of D can be challenging and thus, sufficient for

facilitating answerability. Nevertheless, it must be noted that

definition of the sensitivity and specificity of IM is a prerequisite for a

positive or a negative answer. Accordingly, the research question




                                      4
arising is whether the sensitivity and specificity of modality IM is

higher than those of the modality A for diagnosing D.

      With regard to ethics, a properly posed research question should

be characterized by three substantial principles: I) respect for people,

II) beneficence, and III) justice (Hulley and Cummings, 1988). With

respect to the first principle, all study subjects after being informed

about the potential risks and benefits of the study sign a consent form.

Cooperation between the researcher and the subjects is only attained

when the latter do not feel like objects to be studied, but rather like

collaborators and contributors who volunteer for the humanity well-

being. The research question is beneficent when the benefits of the

research are proportionate to the potential risks of the subjects. The

even distribution of the benefits and burdens of research to all people

with no discrimination regarding physical disability, races, and

imprisonment status characterizes an ethical research question. In

accordance to the ethics of the study, it is also the responsibility of the

researcher to conceal the identity of the people willing to be study

subjects and thus, preserve patients’ confidentiality. In terms of

academic honesty however, deviations from good research practices

may place intellectual integrity at increased risk for misconduct and

violation. Fabrication of fictitious data or results, falsification and

selective, non-scientific presentation of information, plagiarism and



                                      5
forgery of the ideas of other investigators represent deliberate and

serious forms of academic deceit.



THE STUDY DESIGNS

Given that the study design is the methodology for answering the

research question, an understanding of the study design is important

in analyzing the concept of a research protocol. Prospective studies

provide more explicit data as all the subjects undergo a determined

protocol and the data are collected uniformly. Conversely,

retrospective studies are characterized by a lower cost and are

definitely less time-consuming processes.

      In a cohort study, which is well-accepted as the most

scientifically sound type of study, the subjects are followed over a

certain period of time in order to describe the incidence or natural

history of a condition, and to analyze the risk factors as well as the

confounding factors (Hulley and Cummings, 1988). It is not surprising

that the cohort study requires a prolonged study time, enough to allow

the condition to develop, as well as numerous study subjects. The

measurement of the risk of an outcome relative to whether a

predisposing factor is present, known as the relative risk (rr) and the

odds ratio is of particular interest in medical research. The relative

risk of the disease or the risk ratio can only be calculated from cohort



                                    6
studies. It represents the ratio of incidence in persons that have been

exposed to the predisposing factor (risk group) to incidence in those

who have not been exposed to the predisposing factor (control group).

The relative risk can be estimated by the following formula:


             total number in risk group with outcome
                      total number in a risk group
 rr =       total number with outcome in control group
                  total number in control group




The odds ratio is the odds that a patient is exposed to the risk factor

divided by the odds that a control is exposed (Prentice et al, 1975).

        In the cross-sectional study, both the dependent and the

independent variables are measured at a single point in time. By

comparison to the cohort study, a cross-sectional study may be less

time-consuming and may even cost less, but unfortunately, the chance

for error is increased. In a case-control study however, a

retrospective analysis of the prevalence of risk factors in a sample of

patients defined as the cases, is compared to the prevalence of risk

factors in a sample of people free of disease, defined as the control

group (Hulley and Cummings, 1988). Not uncommonly, in radiology

research involves the evaluation of imaging diagnostic methods. In




                                    7
this setting, diagnostic methods are usually appreciated with

randomized blinded trials.



THE STUDY POPULATION

The next step to be taken is the determination of the study population,

that is to specify the group of patients in whom the research question

has to be answered. In specific, in our theoretical example the

research question arising is whether sensitivity and specificity of IM

are higher than sensitivity and specificity of modality A for diagnosing

D in the patient population P. For the purposes of the study, the

target population needs to be defined by stating the clinical and

demographic features of the subjects included. Not infrequently, initial

definition of the target population ends up in a large number of

patients that needs to be remarkably further eliminated. With the

definition of inclusion or selection criteria such as the age range,

gender, geographic location and time, clinical symptoms, laboratory

findings, type, stage, and severity of the disease, the number of

patients eligible for the study, constituting the accessible study

population is determined.

      Although the accessible population by and large meets the

inclusion criteria set for the study, it may still be too large to be

studied. For this reason, a sampling method resulting in the intended



                                      8
sample needs to be applied. Indeed, numerous sampling methods

ranging from random sampling to judgemental sampling exist.

However, a randomized controlled study design should always be

considered when the research question concerns the evaluation of a

new diagnostic method (Hulley and Cummings, 1988). Therefore, the

study design selected, as well as the reason for its choice should also

be clearly stated.



TYPE OF SAMPLING

It becomes obvious however, that each time the selection of the most

appropriate type of sampling depends on the research question. It is

not surprising that the judgemental sampling introduces selection bias

to the research. It is noteworthy however, that consecutive sampling

approximates random sampling, in a fashion that the next series of

patients to be included in the study is already predefined. Indeed,

random sampling may deal with confounding factors such as the

existence of a second illness, patient's uncooperativeness which in

fact, may influence the other variables being studied. Finally, a

recruitment strategy maximizing the number of patients eligible to be

actually participating in the study, is also required. Overall, the study

population should be representative in terms of that the findings in the

actual sample should be applicable to the target population, a feature



                                    9
of the study well-known as generalizability. When the actual sample

does not reflect the target population itself, a serious error known as

sampling error, occurs. Indeed, sampling error maybe systematic and

thus, may alter the study findings.

      In this setting, the intended sample may be improperly defined

or there may be recruitment bias in the actual sample. Likewise,

sampling error may be random owing to sample selection. For this

reason, large study populations are considered especially well suited

for the elimination of random error. An obvious limitation to a

retrospective study however, is the development of an appropriate

study population, as the investigator is practically unable to control the

inclusion criteria set for the study. When writing up an article

including observations about a certain entity in a series of patients, it

is fundamentally important for the materials and methods section to

be written early, while the study is being designed. The benefit is two-

fold as inclusion criteria to the study population have to be carefully

outlined from the very beginning and the researcher is prompted to

think thoroughly through the methods.



THE STUDY VARIABLES

In a thoughtfully designed study, it is useful to identify which variables

are dependent, independent, and interfering (confounding). For



                                      10
example, included among dependent variables are the clinical

outcome, while included among independent variables are the age,

gender, and clinical symptoms of the patient, which indeed represent

factors being under researcher’s control.

      A variable may be dichotomous, categorical or continuous. A

dichotomous variable represents one of two choices e.g gender (male

or female). A categorical variable is one of several choices e.g race

(white, black, asian etc.). A continuous variable is one of infinite

choices e.g age. The gold standard variable is usually one of the

dependent variables, against which other dependent variables are

compared. An imperfect gold standard variable may introduce biases

into the study results. Specifically, bias occurs when the dependent

variable being evaluated is used to define the gold standard variable

(McNeil, 1991). The measurements of the study are enforced when

precision and accuracy are maximized. Precision describes the degree

to which a variable has nearly the same value each time it is

measured. When there is a high precision, increased statistical power

is produced. Accuracy describes the degree to which the variable

actually represents what it is intended to represent, expressing how

close the measurement is to actual reality. Precision, an indicator of

measurement reproducibility, increases when the variability of the

observer, the subject, or the instrument decrease. In particular, the



                                    11
presence of a standard observer trained in the study methods and the

use of an operation manual may significantly reduce the observer

variability.



VARIABILITY IN CLINICAL STUDIES

The specification of observer/reader population (the radiologists

interpreting the diagnostic test) indicates a whole new dimension in

the problem of assessing diagnostic modalities (Hanley, 1988, Hanley,

1989). It is conceivable that a study involving a select group of

highly-specialized readers would provide accuracy assessment

classified in the upper end in the distribution of accuracies between the

readers’ population nationwide. When the researcher interpretes the

results he should always bear in mind the presence of intra- and inter-

observer variability. Both interobserver variability testing the degree

of agreement among different observers under the same conditions,

and intraobserver variability testing the degree of consistency of a

single observer at different times, are of particular importance.

      Subject variability measured by subjects undergoing more than

one test, may affect study result interpretation. Instrument variability

is quantified by repeat measurements. In addition, refinement and

automation are considered helpful in reducing instrument variability.

The specification of the technical features of the diagnostic imaging



                                   12
modality constitutes a standard part of the research protocol.

Optimally, when participating in a certain study, all patients should

have to be studied using the same imaging technique, unless a

comparison between alternative techniques (e.g use or not of contrast

medium) is to be made.

      To recapitulate, the thorough design of a research study requires

experience, close supervision by an attentive and a dedicated

investigator who will control the methodology protocol, maintenance of

accurate records of research procedures and results, and above all,

abundant time to be invested in the on-going effort. Research findings

and conclusions drawn from the research become available to the

scientific community through open communication and publications.

Particularly, the ideal diagnostic test has to present certain features.

In fact, the diagnostic test has to be quick, not complicated, painless

for the patient, reliable, inexpensive, and sufficient to provide the right

answer (Hulley and Cummings, 1988). In accordance to the

aforementioned criteria, a diagnostic test that already complies with

the majority of them, may prove that the introduction of a new

diagnostic test finally, is not noteworthy.




                                    13
KEY POINTS

• The research protocol is developed to answer the question.

• The research question should qualify the following criteria: I)

importance, II) novelty, III) feasibility to answer, IV) ethics, and V)

relevance.

• An ethical research question should be characterized by respect for

people, beneficence and justice.

• Diagnostic methods are most commonly appreciated with

randomized blinded trials.

• The study population is the group of people from whom data is

collected for the study.



REFERENCES

1. Berwick DM, Feinberg HB, Weinstein MC (1981) When doctors need

   numbers. Am J Med 71:991-8

2. Goldin J, Sayre JW (1996) A guide to clinical epidemiology for

radiologists: Part II statistical analysis. Clin Radiol 51:317-24

3. Hanley JA (1988) Alternative approaches to receiver operating

characteristic analyses. Radiology 168:568-70

4. Hanley JA (1989) Receiver operating characteristic methodology:

the state of the art. CRC Crit Rev Diagn Imaging 29:307-35




                                    14
5. Hulley SB, Cummings SR (1988) Designing clinical research: an

epidemiologic approach. Williams & Wilkins, Baltimore, MD: 1-235

6. McNeil B (1991) Experimental design for clinical studies and the

importance of statistics. Presented at the Conjoint Committee on

Diagnostic Radiology’s 5th

Grantmanship Workshop, November 8-9, Washington DC

7. Prentice C, Forbes C, Morrice S, et al (1975) Calculation of

predictive odds for possible carriers of haemophilia. Thromb 34:740-7

8. Weiss ST, Samet JM (1980) An assessment of physician knowledge

of epidemiology and biostatistics. Am J Med Education 55:692-703




                                   15
16

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20050325 Design of clinical trails in radiology

  • 1. Design of Clinical Trials in Radiology for Improved Assessment of Diagnostic Tests. Stavroula J. Theodorou, M.D., Daphne J. Theodorou, M.D. Department of Radiology; University of California, San Diego, Veterans Affairs Medical Center, San Diego, CA ABSTRACT Proper design of clinical trials has become a prerequisite for both the performance and interpretation of research in radiology as well as in other disciplines in medicine. This paper reviews the process of designing clinical research, the research question, the review of existing data, the study design, the study population, and the study measurements. Theodorou SJ, Theodorou DJ. Design of clinical trials in radiology for improved assessment of diagnostic tests. Internet Medical Journal, 2005, 5:1. http://www.medjournal.com/forum/showthread.php?p=1450 1
  • 2. In recent years, several studies have demonstrated the inadequate level of knowledge and understanding of study design and statistics held by physicians including radiologists (Weiss and Samet, 1980, Berwick et al, 1981, Goldin and Sayre, 1996). Rigorous research begins with the precise definition of the research question, which describes the uncertainty of something observed in the population that the researcher believes can be resolved by making measurements on study subjects (Hulley and Cummings, 1988). THE RESEARCH PROTOCOL The research protocol is the written plan of the investigation that defines the research question, the rationale for the study, the materials and methods to be used in detail, and the anticipated problems that may occur in the execution of the study. Optimally, the steps taken to avoid bias and thus, eliminate the most common reason responsible for the lack of validity should also be described in detail in the study protocol. Ideally, the protocol is evolving and improving during the execution of the study, as the researcher reevaluates and revises its components. A timeline of the expected dates of completion of each part of the study and factors which warrant the feasibility of the study, including financial and other logistical constraints encountered in the research process, should be precisely 2
  • 3. stated in the protocol, as well. Indeed, research funding is one of the major parameters that ensures the feasibility of the research study. In fact, a rigorous and detailed protocol should always be a prerequisite for all clinical trials and in terms of academic honesty, should never aim at the request of research funds, alone. THE RESEARCH QUESTION The research question is developed in a form termed the hypothesis. Hypothesis defines the study design, the sample, and the measurements that need to be made. Good research questions should qualify the following criteria: I) importance, II) novelty, III) feasibility to answer, IV) ethics, and V) relevance. The following research question serves as an example for illustrative purposes. Suppose a new imaging modality (IM) has been developed that provides the radiologist with data concerning the disease (D). The research question inquires whether IM provides information associated with the diagnosis of D. IM would be of any significant value and the research question would prove a good one, if only D is a major health problem resulting in great morbidity, if left undiagnosed. If the diagnosis of D can already be made utilizing other existing imaging modalities or even can be attained on the basis of clinical and/or laboratory findings, then the research question would be of a limited importance. 3
  • 4. Traditionally, this question of importance is also known as the “so what? ” criterion, in terms of why someone should spend his time and money to answer it. With respect to the answer to the research question itself, ideally it has to be novel, so that it can provide additional information to the already existing scientific knowledge or optimally constitute new information. Given the necessity of a thorough investigation of previous studies associated with the present research question, a review of the literature is considered extremely important. However, this certain procedure may lead to the modification of the initial research question, since questions which remain unanswered may be identified. For the purposes of the study, one of the main features of the research question is the answerability, as the research question should be stating the study’s major clinical variables and also be explicit. In the aforementioned example however, the research question is rather vague and as a result it remains unanswerable, necessitating a modification. Indeed, questioning whether IM is sensitive and specific for the diagnosis of D can be challenging and thus, sufficient for facilitating answerability. Nevertheless, it must be noted that definition of the sensitivity and specificity of IM is a prerequisite for a positive or a negative answer. Accordingly, the research question 4
  • 5. arising is whether the sensitivity and specificity of modality IM is higher than those of the modality A for diagnosing D. With regard to ethics, a properly posed research question should be characterized by three substantial principles: I) respect for people, II) beneficence, and III) justice (Hulley and Cummings, 1988). With respect to the first principle, all study subjects after being informed about the potential risks and benefits of the study sign a consent form. Cooperation between the researcher and the subjects is only attained when the latter do not feel like objects to be studied, but rather like collaborators and contributors who volunteer for the humanity well- being. The research question is beneficent when the benefits of the research are proportionate to the potential risks of the subjects. The even distribution of the benefits and burdens of research to all people with no discrimination regarding physical disability, races, and imprisonment status characterizes an ethical research question. In accordance to the ethics of the study, it is also the responsibility of the researcher to conceal the identity of the people willing to be study subjects and thus, preserve patients’ confidentiality. In terms of academic honesty however, deviations from good research practices may place intellectual integrity at increased risk for misconduct and violation. Fabrication of fictitious data or results, falsification and selective, non-scientific presentation of information, plagiarism and 5
  • 6. forgery of the ideas of other investigators represent deliberate and serious forms of academic deceit. THE STUDY DESIGNS Given that the study design is the methodology for answering the research question, an understanding of the study design is important in analyzing the concept of a research protocol. Prospective studies provide more explicit data as all the subjects undergo a determined protocol and the data are collected uniformly. Conversely, retrospective studies are characterized by a lower cost and are definitely less time-consuming processes. In a cohort study, which is well-accepted as the most scientifically sound type of study, the subjects are followed over a certain period of time in order to describe the incidence or natural history of a condition, and to analyze the risk factors as well as the confounding factors (Hulley and Cummings, 1988). It is not surprising that the cohort study requires a prolonged study time, enough to allow the condition to develop, as well as numerous study subjects. The measurement of the risk of an outcome relative to whether a predisposing factor is present, known as the relative risk (rr) and the odds ratio is of particular interest in medical research. The relative risk of the disease or the risk ratio can only be calculated from cohort 6
  • 7. studies. It represents the ratio of incidence in persons that have been exposed to the predisposing factor (risk group) to incidence in those who have not been exposed to the predisposing factor (control group). The relative risk can be estimated by the following formula: total number in risk group with outcome total number in a risk group rr = total number with outcome in control group total number in control group The odds ratio is the odds that a patient is exposed to the risk factor divided by the odds that a control is exposed (Prentice et al, 1975). In the cross-sectional study, both the dependent and the independent variables are measured at a single point in time. By comparison to the cohort study, a cross-sectional study may be less time-consuming and may even cost less, but unfortunately, the chance for error is increased. In a case-control study however, a retrospective analysis of the prevalence of risk factors in a sample of patients defined as the cases, is compared to the prevalence of risk factors in a sample of people free of disease, defined as the control group (Hulley and Cummings, 1988). Not uncommonly, in radiology research involves the evaluation of imaging diagnostic methods. In 7
  • 8. this setting, diagnostic methods are usually appreciated with randomized blinded trials. THE STUDY POPULATION The next step to be taken is the determination of the study population, that is to specify the group of patients in whom the research question has to be answered. In specific, in our theoretical example the research question arising is whether sensitivity and specificity of IM are higher than sensitivity and specificity of modality A for diagnosing D in the patient population P. For the purposes of the study, the target population needs to be defined by stating the clinical and demographic features of the subjects included. Not infrequently, initial definition of the target population ends up in a large number of patients that needs to be remarkably further eliminated. With the definition of inclusion or selection criteria such as the age range, gender, geographic location and time, clinical symptoms, laboratory findings, type, stage, and severity of the disease, the number of patients eligible for the study, constituting the accessible study population is determined. Although the accessible population by and large meets the inclusion criteria set for the study, it may still be too large to be studied. For this reason, a sampling method resulting in the intended 8
  • 9. sample needs to be applied. Indeed, numerous sampling methods ranging from random sampling to judgemental sampling exist. However, a randomized controlled study design should always be considered when the research question concerns the evaluation of a new diagnostic method (Hulley and Cummings, 1988). Therefore, the study design selected, as well as the reason for its choice should also be clearly stated. TYPE OF SAMPLING It becomes obvious however, that each time the selection of the most appropriate type of sampling depends on the research question. It is not surprising that the judgemental sampling introduces selection bias to the research. It is noteworthy however, that consecutive sampling approximates random sampling, in a fashion that the next series of patients to be included in the study is already predefined. Indeed, random sampling may deal with confounding factors such as the existence of a second illness, patient's uncooperativeness which in fact, may influence the other variables being studied. Finally, a recruitment strategy maximizing the number of patients eligible to be actually participating in the study, is also required. Overall, the study population should be representative in terms of that the findings in the actual sample should be applicable to the target population, a feature 9
  • 10. of the study well-known as generalizability. When the actual sample does not reflect the target population itself, a serious error known as sampling error, occurs. Indeed, sampling error maybe systematic and thus, may alter the study findings. In this setting, the intended sample may be improperly defined or there may be recruitment bias in the actual sample. Likewise, sampling error may be random owing to sample selection. For this reason, large study populations are considered especially well suited for the elimination of random error. An obvious limitation to a retrospective study however, is the development of an appropriate study population, as the investigator is practically unable to control the inclusion criteria set for the study. When writing up an article including observations about a certain entity in a series of patients, it is fundamentally important for the materials and methods section to be written early, while the study is being designed. The benefit is two- fold as inclusion criteria to the study population have to be carefully outlined from the very beginning and the researcher is prompted to think thoroughly through the methods. THE STUDY VARIABLES In a thoughtfully designed study, it is useful to identify which variables are dependent, independent, and interfering (confounding). For 10
  • 11. example, included among dependent variables are the clinical outcome, while included among independent variables are the age, gender, and clinical symptoms of the patient, which indeed represent factors being under researcher’s control. A variable may be dichotomous, categorical or continuous. A dichotomous variable represents one of two choices e.g gender (male or female). A categorical variable is one of several choices e.g race (white, black, asian etc.). A continuous variable is one of infinite choices e.g age. The gold standard variable is usually one of the dependent variables, against which other dependent variables are compared. An imperfect gold standard variable may introduce biases into the study results. Specifically, bias occurs when the dependent variable being evaluated is used to define the gold standard variable (McNeil, 1991). The measurements of the study are enforced when precision and accuracy are maximized. Precision describes the degree to which a variable has nearly the same value each time it is measured. When there is a high precision, increased statistical power is produced. Accuracy describes the degree to which the variable actually represents what it is intended to represent, expressing how close the measurement is to actual reality. Precision, an indicator of measurement reproducibility, increases when the variability of the observer, the subject, or the instrument decrease. In particular, the 11
  • 12. presence of a standard observer trained in the study methods and the use of an operation manual may significantly reduce the observer variability. VARIABILITY IN CLINICAL STUDIES The specification of observer/reader population (the radiologists interpreting the diagnostic test) indicates a whole new dimension in the problem of assessing diagnostic modalities (Hanley, 1988, Hanley, 1989). It is conceivable that a study involving a select group of highly-specialized readers would provide accuracy assessment classified in the upper end in the distribution of accuracies between the readers’ population nationwide. When the researcher interpretes the results he should always bear in mind the presence of intra- and inter- observer variability. Both interobserver variability testing the degree of agreement among different observers under the same conditions, and intraobserver variability testing the degree of consistency of a single observer at different times, are of particular importance. Subject variability measured by subjects undergoing more than one test, may affect study result interpretation. Instrument variability is quantified by repeat measurements. In addition, refinement and automation are considered helpful in reducing instrument variability. The specification of the technical features of the diagnostic imaging 12
  • 13. modality constitutes a standard part of the research protocol. Optimally, when participating in a certain study, all patients should have to be studied using the same imaging technique, unless a comparison between alternative techniques (e.g use or not of contrast medium) is to be made. To recapitulate, the thorough design of a research study requires experience, close supervision by an attentive and a dedicated investigator who will control the methodology protocol, maintenance of accurate records of research procedures and results, and above all, abundant time to be invested in the on-going effort. Research findings and conclusions drawn from the research become available to the scientific community through open communication and publications. Particularly, the ideal diagnostic test has to present certain features. In fact, the diagnostic test has to be quick, not complicated, painless for the patient, reliable, inexpensive, and sufficient to provide the right answer (Hulley and Cummings, 1988). In accordance to the aforementioned criteria, a diagnostic test that already complies with the majority of them, may prove that the introduction of a new diagnostic test finally, is not noteworthy. 13
  • 14. KEY POINTS • The research protocol is developed to answer the question. • The research question should qualify the following criteria: I) importance, II) novelty, III) feasibility to answer, IV) ethics, and V) relevance. • An ethical research question should be characterized by respect for people, beneficence and justice. • Diagnostic methods are most commonly appreciated with randomized blinded trials. • The study population is the group of people from whom data is collected for the study. REFERENCES 1. Berwick DM, Feinberg HB, Weinstein MC (1981) When doctors need numbers. Am J Med 71:991-8 2. Goldin J, Sayre JW (1996) A guide to clinical epidemiology for radiologists: Part II statistical analysis. Clin Radiol 51:317-24 3. Hanley JA (1988) Alternative approaches to receiver operating characteristic analyses. Radiology 168:568-70 4. Hanley JA (1989) Receiver operating characteristic methodology: the state of the art. CRC Crit Rev Diagn Imaging 29:307-35 14
  • 15. 5. Hulley SB, Cummings SR (1988) Designing clinical research: an epidemiologic approach. Williams & Wilkins, Baltimore, MD: 1-235 6. McNeil B (1991) Experimental design for clinical studies and the importance of statistics. Presented at the Conjoint Committee on Diagnostic Radiology’s 5th Grantmanship Workshop, November 8-9, Washington DC 7. Prentice C, Forbes C, Morrice S, et al (1975) Calculation of predictive odds for possible carriers of haemophilia. Thromb 34:740-7 8. Weiss ST, Samet JM (1980) An assessment of physician knowledge of epidemiology and biostatistics. Am J Med Education 55:692-703 15
  • 16. 16