research:-
an scientific effort to find solution to a problem.
if there is no problem, research is not needed.
research problem:-
when there is a discrepancy between what is and what should be i.e. between a present non satisfactory situation and a future ideal satisfactory one.
it could be a basic science problem
(biochemical, bacteriological, biomaterial…ect)
it could be a clinical problem (diagnostic test, treatment efficacy, patient management or health care delivery system proplem).
the solution may become in the future a non satisfactory situation and research will again be needed.
three kinds of papers published in journals:-
research reports… reports of original clinical basic or epidemiological research.
review of literature… summarize knowledge in a particular areas.
commentaries, where some documented facts are used as basis for program development.
secondary scientific papers:-
is a review paper which summarize other paper.
2 types of review:-
narrative review in which the studies reviewed have not been identify or analyzed.
systematic review, it contain explicit statement or objectives with spelt out research question.
the data source are stated as well as the methods of selection.
research conducted according to an explicit methodology
a systematic review includes
abstract.
introduction:- a well clear systematic review answers a questions or closely related questions, which should be made clear at the beginning of the review.
methods:- should fully describe the methods used for locating , selecting, extracting and synthesizing the data.
body of the review :- the sequence should have logical basis. the argument should ecritical.
meta - analysis
a special type of systematic review that combines results from more than one investigation to obtain a weighted average of the effect of a variable or intervention on a defined outcome.
combining data increases sample size and the power of the study to provide statistically significant conclusions.
effect size:-
degree to which the event is present in the population.
it is based on mean if the outcome is numerical comparison, on proportion or odd ratio or relative risk if the outcome is nominal and on correlation if the outcome is an numerical association.
effect sizes themselves are combined in meta analysis.
e.g.: calculate the odd ratio and 95% c.i for each study.
use meta analysis method to determine summary odd ratio over all the studies.
study design:-
health research studies may be broadly divided as follows:-
non intervention studies, where the researcher just describes and analyzes researchable objects or situations but does not intervene.
intervention studies ,where the researcher manipulates objects or situations, either by preventive or therapeutic measures, and determine the outcome of his manipulation.
non intervention studies:-
are further classified into three types of studies. exploratory studies:-
is a small scale study of relatively short duration, which is carried out when little is known about a situation or problem.
it can describe needs of various categories of patients and the possibilities for action.
it can also go further and try and explain the differences observed.
descriptive studies:-
involves the systemic collection and presentation of data to give a clear picture of a particular situation. involve 3 types.
descriptive case studies:
in-depth description of the characteristics of one or limited number of cases (patients, health center, village, community).
cross-sectional studies:-
quantification of the distribution of certain variables in the study population at one point of time.
it may quantify the demographic variables(age, education, gender…ect) and the events that has occurred in the population.
such study called prevalence study.
longitudinal studies:-
is one in which the same group of people is studied on two or more occasions to determine the progress of the condition.
such study also call incidence study.
dental caries increment could be determine through that study.
causality & risk
causality meaning that certain exposure results in a particular outcome. analytical studies have the general aim of seeking out cause and effect association.
it cannot directly adresses cause and effect, they seek to quantify the degree of disease risk in specified circumstances.
risk means the probability that a specified event will occur, e.g disease or death.
risk factor is defined as an attribute or exposure that is known, from epidemiologic evidence, to be associated with a health condition can be modified and considered important to prevent.
risk factor for a disease must be demonstrated as such longitudinally.
if a suspected r.f cannot be confirmed as such because the necessary longitudinal studies are impractical or unethical, the factor may be classed as a risk indicator.
risk indicator is a factor shown to be associated with a disease in cross sectional studies.
research experience has shown that risk indicators which ensure from cross sectional studies can disappear in more rigorous longitudinal analysis indicating that it is not a true r.f.
risk marker is an attribute or exposure that is associated with the increased probability of disease although it is not considered part of the causal chain.
it also be called a risk predictor when included in predictive statistical model whose purpose is to predict disease occurrence
recently the term demographic r.f. is use to refer to these factors such as age a, gender, race and socio-economic status.
they clearly are of no use when considering disease prevention as they are not modifiable.
the following conditions must be satisfied before particular exposure can be accepted as the cause of a disease called the bradford hill criteria. it can be reached from non experimental epidemiologic analysis.
1-the sequence of events:- to be causal, an exposure must precede the occurrence of a disease which need longitudinal study to demonstrate it.
2-consistency of association:- good number of studies proved that with fairly similar positive results.
3-strength of association statistically:- in valid studies, the stronger the association between exposure and outcome, the more likely it is that the association is causal.
4-specificity of association:- if a given exposure is related to other disease as well as the disease in question, it is less likely to be seen as causal. however, lack of specificity by itself does not justify rejecting causality.
5-degree of exposure (dose response) that is the risk of disease should be related to the degree of exposure except toxin.
6-biologic plausibility:- association must make biologic sense from our knowledge of the disease.
7-absence of error:- the observed association must not be the result of error, whether that be bias, sampling error, analytical errors, or the intrusion of other extraneous factors (confounding factors).
the most important factors are:-
time sequence.
statistical association.
absence of error.
analytical studies:-
analytical studies attempt to determine association between disease and possible risk factors or demographic r.f., and to quantify the degree of risk.
the determination of risk factors for a disease allows the potential for preventing the disease by removing or modifying the risk factors.
types of analytical studies:-
a-cohort study (prospective study).
observational analytic design, in which group of individuals are defined on the basis of presence or absence of exposure to a suspected risk factor for a disease.
the participants are then followed over a period of time to assess the occurrence of that disease.
aiming to provide sound evidence of whether there is a valid statistical association between exposure and disease.
advantages of cohort study:-
allow the investigator to examine a large number of hypothesis at one time.
gives valid results.
disadvantages:-
take time to get the outcome data.
very expensive (long time).
sample size must be large (droping out??)
longitudinal=incidence=cohort study prospective study
condition
exposure +
+
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+
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prospective cohort study. non experimental
analytical, typical cohort study.
ask question ”what will happened”
longitudinal.
droping out bias.
historical cohort or retrospective cohort studies.
by using information collected in the past and kept in records or files.
the event being evaluated actually occurred before the onset of the study. the cohort of subjects has been assembled for other purpose.
direction of inquiry is still forward in time, from possible cause or risk factor to an outcome.
b-case- control study (retrospective)
are relatively simple and economical to carry out, commonly used to investigate causes of rare diseases.
it include people with a disease of interest (case) and suitable unaffected group (control).
investigator collects information on exposure history from diseased study subjects (case) and non diseased (control).
aiming to provide sound evidence of whether there is a valid statistical association between exposure and disease.
case-control study=retrospective study
exposure
+
_
+
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case – control study. non experimental
analytical study that ask “what happened”.
begin with the absence or presence of an outcome, then look backward in time (retrospective) to try to detect possible cause or risk factor.
matching concept is essential to be sure that both groups will be similar with respect to important variables that may otherwise cloud or confound the conclusion.
longitudinal.
recall bias.
experimental studies:-
clinical trial:- are carried out among patients, frequently hospital in- patients.
(therapeutic t.intervention t, and preventive t)
field trial:-are carried out with people in the community who may not necessarily be patients.
clinical trial:-
is a controlled experimental study of group of comparison.
it designed to test the hypothesis that certain agent or regimen favorably alter the natural history of a disease experience.
it compare two or more segments of a single population.
essentially they must be similar in distribution of age, gender, race, ses and disease.
the group receiving the agent or regimen under study is the test group.
the comparable group which not subjected to the agent or regimen is the control group.
factors affecting the validity the trial:-
random assignment to study and control groups will give a confidence that the groups are comparable, which prevent bias of data.
bias:- errors and mistakes that can happen during the study by:-
the investigator.
the participants.
the assessment and outcome.
provide the control group with placebo, which is a substance similar in appearance and all properties to that being tested except in respect to the active ingredient.
apply the concept of blind or double blind assessment, nowadays tertiary blind.
adequate number of subjects for the attrition, least researcher will fail to show by statistical tests whether a difference exists between the group.
reliability in diagnosis can be achieve by the inter & intra examiner reliability tests.
clinical trial must be continued long enough to permit detection of new disease or extension of lesion already present during the trial.
for caries trial, minimum duration 2 years.
for plaque inhibiting agents trial, 8-21 days.
to demonstrate gingivitis reduction, 6 month.
for calculus preventing agents should last 90 days for supra gingival calculus & longer for sub gingival calculus.
there are two types of true experimental designs, whether the treatment comparisons are made either between subjects (parallel group designs) or within subjects (matched designs or cross – over designs)
both are considered as clinical trial.
the researcher assigns different therapeutic measures to different groups of subjects in the study.
the unit of investigation is the individual.
controlled clinical trials:-
in which the experimental drug or procedure is compared with another drug or procedure, sometimes a placebo and sometimes the previously accepted treatment.
the researcher randomly assigns some patients to the experimental condition and others to the placebo or standard condition.
which are called concurrent controls
if the same group of study subjects are use for both experimental and control procedures, it is designated as a self- controlled clinical study design .
randomized crossover study design:-
crossover designs are often applied to chronic conditions (palliative rather than curative) such as recurring gingivitis, where outcome is measured in terms of short term relief of signs and symptoms.
several design features of the randomized crossover clinical trial are important to recoqnize.
first, a pre-randomization run- in period is usually required. during this period the patient commonly receives a placebo treatment, such as standard prophylaxis and oral hygiene instruction, and the condition of the entire study sample is monitored until the physiological condition of each patient has reached a stable baseline.
at that point each patient is scheduled to receive a sequence of both the experimental and control treatment, but in opposite order, thus signifying the cross over character.
second feature is that a wash-out period is needed after the treatment has been stopped to allow each patients physiological condition to return to its baseline level.
this period should be long enough so that the therapeutic effect of the first treatment does not carry over into the second treatment time period.
experimental studies c.t
1-controlled trial:
a. trial with independent control.
randomized (rct)
non randomized (cct)(comparative study)(bias)
pseudorandom mechanism.
2-trials with self control:
before and after.
split mouth technique.
cross – over design.
3-trial with external control:
using result of another investigator as a comparison.
4-quasi experimental design:
when u choose a non equivalent control group so as to match the study group as closely as possible.
pop1…sample…formocersol.
pop2…sample…ferric.
5-uncontrolled studies.
factorial design:-
aims to answer two or more separate research questions in single cohort of participants.
e.g effect of low dose of aspirin, vit e on risk of cardiovascular events on healthy women.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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