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Reading an article
1. Dr Nahid Sherbini
Consultant Internist & Pulmonologist
Certified from Harvard Medical School in Practice of Clinical
Research
2. Outlines
Contents of a research paper
BASICS OF CLINICAL RESEARCH ARTICLE
• Introduction to Clinical Trials
• Study Questions
• Study Population
• Basic Study Design
• Study Blinding
• The Randomization Process
• Recruitment of Study Participants
BASIC STATISTICS
3. • Title
• Author’s name and affiliation
(Byline)
• Abstract
• Keywords
• Introduction
• Literature review
• Method
• Results
• Discussion
• Conclusion
• References
• Acknowledgements
• Biographical sketch
• Appendices
3
4. Clear and explanatory title
An incomplete sentence
Brief and concise
4
5. Miniature of the text
150 to 200 words
Paragraph or structured
Descriptive or informative
Complete concise sentences
Contents of Abstracts:
Purpose or scope of the paper
Methods
Results, conclusions and recommendations
6
6. Identifies subject area of interest
States the purpose and hypothesis of the study
Provides a statement of the rationale for approach to the problem
studied.
8
7. Establishes context of the study by providing a brief and balanced
review of pertinent published literature available on subject.
General to specific
Name-date citations
9
8. Study design
Participants and their characteristics
When and where study conducted
Sampling method and size
Variables measured
Method of collecting data
How data analyzed: Statistical procedures used
10
9. Objective presentation of key findings without interpretation
Orderly, logical sequence using text and illustrations (figures/tables)
11
10. Answers questions posed in introduction
Interprets results in comparison to what is already known on the subject.
Explains new understanding of the subject based on present results
It tells the readers how present study moved from what was known to
what is new
Outlines limitations of the study
Discusses ideas for future research
12
12. Complete citations for research cited
References are listed in alphabetical order by the first author’s last name
Citations according to style manual, e.g., APA, MLA, Chicago, etc.
14
13. Included as needed
Significant help in thinking, designing, implementing, materials supplied
etc.
Funding agency.
15
15. Phase I
Normal Volunteers
Safety
Dose-Kinetics
Action
Phase II
Patients
Evidence of Activity
Dose
Phase III
Phase IV
Post marketing
Expanded Indications
Safety Studies
16. Phase I
12 - 18 months, 200 volunteers
Phase II
1.5 – 2.5 years, 300 - 500 patients
Phase III and beyond
3 – 4 years, 2000 – 3000 patients
17. Who
Normal physiology
Pathophysiology: rare/severe versus common/complex
What
Observational: retrospective or prospective
Interventional: better
Study Questions
18. Primary question
Most relevant question; sample size
Secondary questions
Can help to clarify the primary question
“Exploratory” or “hypothesis generating”
Insufficient statistical power
Multiple comparisons penalties (type I error)
Ancillary questions
A sub-study within the primary study
Limited generalizability
Study Questions
19. Dependent: outcome
Independent: intervention, predictor
Covariate: may influence the relationship between dependent and independent
variables
Surrogate: more “accessible” outcome, feasible, safe, cost-permissive
Research variables:
22. POPULATION:
Target population: the group of individuals you want to
study
Accessible population: sub-set of individuals that are
available
Study population: included in the study, your sample
Ideally all should have equal characteristics
Study Population
24. Validity
INTERNAL VALIDITY:
Observed results are unbiased estimates of
the relationship between exposure and
outcome
Threats: confounding and bias (e.g. selection
bias, recall bias, detection bias)
May be affected by randomization, allocation
concealment, blinding , study population
25. EXTERNAL VALIDITY:
Unbiased estimate of the relationship between
exposure and outcome in the target population
Generalizability of your findings
Population from you draw your sample
(accessible population) is representative of the
target population
Threats: sampling bias, strict inclusion criteria
Internal validity has to be guaranteed
Validity
26. Homogeneous sample: good for internal, not good for external
validity
Large sample size: not necessarily good for external validity
Broad inclusion criteria: good for external validity
Random sampling: can improve external validity
Important to define inclusion and exclusion criteria: who is in and
who is not in the target population
INTERNAL AND EXTERNAL VALIDITY:
27. Process by which persons from the accessible population become
part of the study population
Study population = random sample of the accessible population =
representative of the target population
Threats: sampling variability or sampling error (by chance, not
bias)
SAMPLING:
28. Probability sampling: at random
Simple random sampling
Systematic sampling
Stratified random sampling
Disproportional sampling
Cluster/multi-stage sampling
Non-probability sampling: not random, most common
Convenience sampling
Snowball sampling
SAMPLING:
29. STUDY DESIGN:
The ultimate goal:
Eliminate systematic error (bias)
Minimize random error (chance, variability)
Ensure the generalizability of study findings
Types of design:
Parallel
Cross-over
Others
Study
Design
30. 32
Other Parallel Groups Designs
R
a
n
d
Plac
Exp
R
a
n
d
Std
Exp
R
a
n
d
Std
Exp
R
a
n
d
Std + Plac
Std + Exp
R
a
n
d
Std
Exp
Exp
Test of Timing
Test of Combination Treatment
Std
Test of Switching
31. FACTORIAL DESIGN:
An example 2 x 2:
Pros: efficiency, test more than one hyphotesis
Cons: possibility of interaction
Threats: if there is interaction you can get misleading results
Placebo Drug A
Placebo Placebo + Placebo Placebo + Drug A
Drug B Drug B + Placebo Drug B + Drug A
32. CROSSOVER DESIGN:
Pros: each subject serves as his/her own control
Cons: possibility of carry over effect or order effect
Washout period may be needed
R
a
n
d
Std
Exp
Exp
Std
Period 1 Period 2
33. BIAS:
May be introduced by study personnel and subjects
If you “know” subject allocation you are susceptible to bias
Intentional or non-intentional
Blinding/masking may reduce the risk
34. TYPES OF BLINDING:
Open label: both the patient and the investigator know allocation
Single blind: patient does not know
Double blind: both the investigator and the patient do not know
Triple blind: both the investigator , the patient, and the
sponsor/statistician do not know
All study personnel should be “blinded”
35. TO ENSURE BLINDING:
When possible make the different study treatments be
identical in appearance, touch, taste, and smell
Have an physician/healthcare provider delivering the
treatment different from physician examining for efficacy
Have an physician examining patient for AEs different from
physician examining for efficacy
Choose an efficacy outcome that is difficult to introduce bias
(e.g. survival)
The packet with the drug contains a label with just the
patient ID
36. Treatment allocation schemes should:
Remove investigator bias in the allocation of participants
Produce treatment groups comparable with respect to known and
unknown risk factors
Guarantee that statistical tests have valid significance levels
Only randomization achieves all three goals
37. Simple/unrestricted randomization: assigns patient to treatment
randomly independently of all other treatment assignments
Cons: long runs, imbalances
Pros: easy
Blocked randomization: block size is a multiple of number of
treatments
Pros: maintains balance
Cons: you can guess the 4th and sometimes the 3rd position
Random block sizes: e.g. 4 or 6 or 8 (for two treatments)
Pros: maintains balance, impossible to guess next allocation
Cons: more complicated
Randomization
38. Stratified randomization:
Patients characteristics (age group, gender, disease severity, etc)
Study center (multicenter trials)
Use limited number of strata
Pick the most important categorical variables
Consider using statistics to “bypass” imbalance of important
variables
Randomization
40. 1. Understanding of study inclusion & exclusion criteria
2. Identification of potential participants
3. Screen for eligibility
4. Obtain informed consent
5. Enrollment into study
41. Burdens
Issues that make enrollment difficult
Barriers
Issues that will prevent enrollment
Benefits:
Medical, financial, altruism
Risks:
Medical: Side effects, assignment to placebo, lack of efficacy
Logistical: Trade off with other time commitments, medical or opportunity
costs
RECRUITMENT:
42. Pool of potential candidates shrinks as it goes through
progressive screens
85-90% of patients in practice will not be eligible for
trial
Total Patients in
Group
Patients found ineligible due
to co-morbidities, lab values
100%
50%
10-15%
Patients Eligible
Fedor, C.; Cola, P. & Pierre, C., D. Responsible Research. p108-9. 2006.
Patients ENROLLED
2-5%
43. Drop outs or premature withdrawals:
Threaten statistical power of the trial
Can introduce bias if drop outs are not randomly
distributed across treatment groups
Necessitates that sites access AE and mortality
status via alternate mechanisms where appropriate
Threaten perception of the trial results
44. “The extent to which the patient continues the agreed-upon mode of
treatment under limited supervision when faced with conflicting
demands”
Examples of non-adherence:
Taking an incomplete/incorrect dose
Taking medication at wrong time
Forgetting to take medication
Stopping the medication before instructed
ADHERENCE
:
45. Non-adherence to follow-up: impact data quality and interpretation
Non-adherence to regimen: impact the power of the study to detect a
clinical effect or potentially effective treatment
Example: changes in dose amount and timing
Adds variance to the outcome
Drug effectiveness may be underestimated
AE may be underestimated
Sample size must increase
Longer/delayed trails
Increased costs
ADHERENCE
:
46. Why is Adherence Important?
- Threatens the ability to complete study
- Misinterpretation of data
- Complicates statistical analyses (ITT vs per protocol)
- Links to drug failure are less clear
- Prolongs studies
- Increased sample size
- Inflates costs
47. NON-ADHERENCE FACTORS:
Participants
Treatment Regimen
Disease and Study Specific Issues
ENHANCING ADHERENCE:
Pre-randomization screening
Run-in period
Test dosing
48. Statistics
TYPE OF DATA:
Qualitative/categorical
Nominal: unordered categories
Ordinal: ordered categories
May be more clinical relevant
Quantitative
Discrete: magnitude and order matters; only specified values
Continuous: not restricted to specified values
Interval scale: zero value is NOT meaningful
Ratio scale: zero value is meaningful
49. MEASURES OF CENTRAL TENDENCY:
Mean: best for normal distributions, sensitive to outliers
Median: best for asymmetric distributions (non-normal)
Mode: best for qualitative data
MEASURES OF DISPERSION:
Variance: sum of the squared deviation of each score from the
mean / N-1
Standard deviation: squared root of the variance
Range, interquartile range (P25th - P 75th), standard error (SE), 95%
confidence interval (CI)
50. TYPES OF TESTS:
One tailed OR two tailed
Direction of the difference known?
Parametric OR non-parametric
Random sampling?
Continuous data (interval or ratio scales)?
Normal distribution?
Equal variances (homogeneity)?
51. Type of data: continuous vs. categorical data
Data distribution: normal vs. non-normal distribution
Number of groups: 2 groups vs more than 2 groups
Type of measures: repeated measures?
What you are looking for: difference vs association vs
prediction
WHAT DO YOU NEED TO KNOW
:
52. Continuous data
Categorical /
binary
Normal
distribution
Non-normal
Compare two groups
(independent variable
- binary)
Unpaired and
paired t-test
Mann-Whitney
Wilcoxon
Chi-square
Fisher’s exact
Compare three or
more groups
(independent variable
- categorical)
ANOVA (one
or n-way
ANOVA)
Kruskal-Wallis
or Friedman
test
Chi-square
Fisher’s exact
Association between
two variables
(independent variable
- continuous)
Pearson
correlation
Spearman
correlation
Association between
three or more
variables
(independent variable
- continuous)
Multiple linear
regression
Multiple
logistic
regression
53. Continuous
(Normal)
Continuous
(Non-normal)
Dichotomous Multi-
Categorical
Failure Time
1
group
1 sample T-test Chi Sq.
(Fisher’s Exact)
Chi Sq.
(Fisher’s
Exact)
2
groups
T-test
Paired T-Test
Wilcoxon Rank
Sum Test
Chi Sq.
(Fisher’s Exact)
McNemar’s
Test
Chi Sq.
(Fisher’s
Exact)
Log-Rank
>2
groups
ANOVA
Linear
Regression
Kruskal Wallis Chi Sq
(Fisher’s Exact)
Logistic Reg.
Chi Sq.
(Fisher’s
Exact)
Logistic Reg.
Log-Rank
Cox Regresion
54. EXAMINE NORMALITY:
Mean = Median = Mode
Skewness and kurtosis
Graphical Assessment
Statistical Tests:
Kolmogorov-Smirnov
Shapiro-Wilk
Normal (Gaussian) Distribution
0
0.05
0.1
0.15
0.2
0.25
2 3.6 5.2 6.8 8.4 10 11.6 13.2 14.8 16.4 18
Probability
Density
55. When does it matter?
Continuous outcome
Small – moderate sample size
Significantly non-normal data
Expected effect size is small
Non-parametric options not available
What are the risks?
Erroneously use parametric tests when data is non-parametric?
False positive results
Erroneously use non-parametric tests when data is parametric?
False negative results (unlikely)
Data Classification in Clinical Research & Sample Size Calculation, Munir Boodhwani, MD, MMSc, FRCSC
56. ANOVA:
Parametric test
Means ANalysis Of VAriance
Compares more than two means/groups
If H0 is rejected, then multiple comparisons/ contrasts between groups
are needed
Post hoc tests: LSD test, Tukey’s HSD, test, Scheffe’s test, Bonferroni
Assumptions: observations are independent, normally distributed data,
homogeneity of variances
57. “OTHERS” ANOVA:
RM ANOVA: Repeated Measures for each subject
(e.g. longitudinal study)
Two-way/factorial ANOVA: two independent variables; main effect +
interaction effect (e.g. study treatment interaction)
ANCOVA: “ANOVA + regression”; comparing means among different
groups while controlling for covariates
58. REGRESSION
Studies the relation between a predictor variable (x) and a response
variable (y)
Both dependent and independent variable are continuous
Can the independent(s) variable(s) predict the dependent variable?
Yi = β0 + β1 Xi
+ ε
Outcome for patient
Dependent variable
InterceptSlope
Predictor/regressor
Independent
variable
Error
term
“noise”
59. Correlation quantifies the degree that two variables are related.
Correlation coefficient (r) = how much one variable tends to change when the other
one does.
Linear regression finds the best line that predicts Y from X.
HMS-CME Principles and Practice of Clinical Research
60. CORRELATION:
Quantifies the degree that two variables are related
Does not mean causation
Pearson product-moment correlation (P)
Spearman's rank correlation (NP)
Correlation coefficent: measures the relationship [r or rho (ρ)]
0 - 0.25 - little or no relationship
0.25 - 0.50 - fair relationship
0.50 - 0.75 - moderate relationship
>0.75 - good to excellent relationship
-1 or 1 - perfect correlation !
61. Usually used as secondary analyses
Correlation coefficient is important to be reported – strength of association
Does not depend on values expressed by x or y and also order does not matter
Correlation is different than causation
Correlation measures linear association (there might be a quadratic association)
Correlation is sensitive to outliers
62. Let us analyze together
Scenario 1 – you have a large sample size:
Using central limit theorem, parametric tests can be used
Differences in p-value are very small when using non-parametric testing
Scenario 2 – you have a small sample size:
Central limit theorem does not apply for parametric tests
Non-parametric tests lack power for small sample sizes
7 or fewer values, mann-whitney is always >0.05
5 or fewer pairs, wilcoxon sign rank is always > 0.05
63. HYPOTHESIS TESTING:
Determines the degree to which your study result can be explained by
chance or sampling variability
A statistically significant difference means it is unlikely due to chance;
not the same as clinical significance
The hypotheses should be defined a priori
Null hypothesis: a=b, treatments are equal
Alternate hypothesis: a ≠ b, treatments are different; difference can be
1-side/direction or 2-side (both directions)
64. AFTER RUNNING YOUR TEST:
Reject null hypothesis: the treatments are different
p value < level of significance
OR
Fail to reject the null hypothesis (“accept the null hypothesis): the
treatment are similar
Attention to the double negative!!!
p value > level of significance
65. Unobserved Truth
in the Population
Ha: Coffee prevents DM
H0: No
association
Observed
in the
Sample
Reject H0:
Treatment
are
different
True positive
(1 – β)
False positive
Type I error (α)
Fail to reject
H0:
Treatments
are similar.
False negative
Type II error (β):
True negative
(1- α)
66. ERRORS IN HYPOTHESIS TESTING:
Error type I
False positive
= probability of committing an error type I
Error type II
False negative
= probability of committing an error type II
1- = power = probability of detecting a difference when one truly exists (true
positive)
67. α (alpha)
aka level of significance
Usually 0.05 (5%)
Probability of type I error (false positive) : rejecting null hypothesis
when it is in fact true
Risk of providing a treatment that actually does not work
β (beta)
Probability of type II error (false negative): failing to detect a difference
when it actually exists
Usually 0.2 (20%)
Risk of not offering a treatment that in fact works
p – value
probability of obtaining a result as extreme or
more extreme than you found in your study by
chance alone
68. Regardless of the statistical procedure, sample
size formulas rely on the same parameters
1. Significance level (α)
2. Desired power (1 – β)
3. Measure of variation of the outcome variable – Ie:
standard deviation (σ)
4. Anticipated treatment/exposure effect (Ha)
69. Screen the published literature: original papers, SR, meta-analysis
Look for SD, variance, 95% CI, standard error, effect size, mean effect
Do a pilot study
Use an analogous study
Expert judgment (clinical meaningful ES)
Minimum Clinically Important Difference (MCID)
HOW DO YOU GET THE DATA YOU
NEED:
70. How sample size changes in response to changes in parameters: α, β,
effect size, measures of variability
Sample size
(total)
Power Incidence rate
intervention
Incidence rate
control
100 73% 10% 30%
200 97% 10% 30%
300 69% 10% 20%
400 81% 10% 20%
400 32% 10% 15%
250 83% 15% 30%
300 89% 15% 30%
400 26% 15% 20%
600 46% 15% 20%
SENSITIVITY
ANALYSIS
71. TRADE-OFFS
Less false positives (type I error) Increase sample size
Less false negatives (type II error) Increase sample size
More power (true positives) Increase sample size
Small exposure effect Increase sample size
More false positives (type I error) Decrease sample size
More false negatives (type II error) Decrease sample size
Less power (true positives) Decrease sample size
Large exposure effect Decrease sample size
72. Use primary outcome
Prefer continuous outcomes (smaller n)
Have balanced samples (more power)
Account for drop-outs
If you have fixed sample sized:
Calculate power a priori: do you really want to do this?
Calculate power post hoc: possibility of a false negative?
SAMPLE
SIZE
73. Time to event data
Not just “survival”: time to rescue medication, time to hospital
admission, etc.
Needs to be defined:
When do you start counting (time origin)
How do measure time (scale)
Define what is your “failure”(event)
Manages “censored” or “incomplete” data
SURVIVAL ANALYSIS:
74. HOW TO DEAL WITH CENSORED DATA:
Not all individuals are observed until they have the event
Censored cannot be related to the probability of the event of interest
Kaplan-Meier Estimation
Numerical: median, 50th percentile, when K-M crosses 0.5 on the y axis
Graphically: survival curve
75. COMPARE SURVIVAL BETWEEN 2 GROUPS:
Without censoring: compare mean time to failure with t-test or Wilcoxon
test
With censoring: log rank test (NP)
CONTROL FOR COVARIATES:
Regression model
Cox Proportional Hazards Regression
Hazard ratio (similar to OR)
76. MISSING DATA:
Important source of bias; reduces power and precision
HOW TO HANDLE IT:
Per protocol (PP), complete-case analysis
Available-case analysis (different n for each analysis)
Weighted procedures (according to likelihood of response)
Intention to treat analysis (ITT)
Single imputation-based procedures:
Mean and median imputation (decrease variance)
Regression imputation (smaller impact on)
Stochastic regression imputation (increase variance)
Last observation carried forward (conservative)
Worst/best case scenario (sensitivity analysis)
Other Issues in
Statistics
77. Missing completely at random: Completely independent of observed and non-
observed data.
Non-missing data constitutes effectively a random sample (example, a rater that becomes sick or
loss of study files)
Missing at random (less stringent): probability of a value being missing will generally
depend on observed values (NOT MISSING VALUES), so it does not correspond
to the intuitive notion of 'random'.
- Old subjects might drop out a treatment because they have walking difficulties – as they
cannot go to the clinic center – however among older subjects, the likelihood of dropping out does not
relate to the outcome.
Missing not at random - present when the pattern of missing data are related to
unobserved data - therefore it is impossible to predict data from other values from
the dataset
Demographic data + baseline performance Follow-up performance
OBSERVED DATA NON-OBSERVED DATA
78. COVARIATE ADJUSTMENT:
Despite randomization there might be imbalances between groups:
e.g. a group might be older and have more females than the other group
[covariates: gender and age]
Advantages:
Improves estimates
Reduces bias
Increases statistical efficiency
Common covariates:
Study center in multicenter studies
Prognostic factors
80. To find out if whether treatment effect is different in patients with a certain
characteristic
Advantages: ideas for new studies, finding groups of patients in whom the
treatment works better
Risks: over interpretation and misleading results; false positives (if p=0.05, 1 in
each 20 comparisons just by chance)
SUB-GROUP ANALYSIS:
81. After primary analysis, often want to look at subgroups
Does effectiveness vary by subgroup?
If drug effective, is it more effective in some populations?
If results overall show no effect, does drug work in subgroup of participants?
Are adverse effects concentrated in some subgroups?
82. SUB-GROUP ANALYSIS versus COVARIATE ADJUSTMENT:
Covariate adjustment: achieve the most accurate p value; increases
precision and power
Sub-group analysis: different responses to the treatment; interaction
between the treatment and a certain characteristic
83. 1. Specified in study protocol have highest validity
Especially if number is small
2. Implied by study protocol
randomization stratified by age, sex or disease stage
3. Subgroups suggested by other trials
4. (Weakest) Subgroups suggested by the data themselves (“fishing” or “data
dredging”)
Example: children under 14 born in October (“month of October victimized by
poststudy analyses biased by knowledge of results”)
5. (Disastrous) Subgroups based on post-randomization variables
84. ?
HOW TO ADDRESS MULTIPLE COMPARISONS:
Bonferroni correction
Fisher’s Least Significance Difference
Duncan
Newman-Keuls
Tukey’s Honestly Significant Difference
Scheffe’s comparison
Disclose error rate (findings by chance alone)
PROBLEM: “overcorrection” increases risk of type II error
85. Meta-analysis refers to the analysis of analyses
the statistical analysis of a large collection of analysis results from individual
studies for the purpose of integrating findings. It connotes a rigorous alternative to
the casual, narrative discussions of research studies which typify our attempts to
make sense of the rapidly expanding literature.
GV Glass (1976). Primary, secondary, and meta-analysis of research. Edu Researcher 5:3-8
META-ANALYSIS:
86. keep up with the enormous amount of research data, judge the quality of
the studies, and integrate findings
Greater precision of effect estimates, and thus reduce probability false
negative results
Consistency of results over different study populations - generalizability
Highlight the limitations of previous studies and contribute to higher
quality of future studies
87. 0. Identification of the need for a review
1. Preparation of a proposal for a review
2. Development of a review protocol
3. Identification of research
4. Selection of studies
5. Study quality assessment
6. Data extraction
7. Data synthesis
8. Report and recommendations
9. Getting evidence into practice
Preparing the review
Reporting/
dissemination
88. Larger studies should be emphasized in the analyses
Weight each ES by its sample size
Weight each ES by the inverse variance (better)
Non-quantitative data synthesis: tables
Quantitive data synthesis: forest plot (OR, ES)
Measure of effect: odds-ratio, risk-ratio, effect size
META-
ANALYSIS:
89. Sensitivity analysis: assess the robustness of the findings
Exclude from the analyses some studies: e. g. older studies, lower quality
studies, extremes of distribution
Heterogeneity: assess variation of outcomes between studies
Cochran’s Q
Publication bias
Begg and the Egger test
Begg funnel plot
META-ANALYSIS:
90.
91.
92. RESEARCH QUESTION
H0: Tight glycemic control will have the same perioperative morbidity
as standard glycemic control
H1: Tight glycemic control will not have the same perioperative
morbidity as standard glycemic control
93. STUDY DESIGN
Interventional
New treatment strategy versus standard care (no placebo)
Randomized and controlled
Multicentric
Phase II trial
95. STUDY POPULATION:
Target population: children 0-36 months undergoing
cardiac surgery with cardiopulmonary bypass
Acessible population: same as above + receiving surgical
treatment Boston and University of Michigan Children’s
Hospital
Study population: same as above + admitted between
September 1006 to May 2012 that were eligible and whose
parents/guardians gave consent
SAMPLING:
Convenience sampling (non-probability sampling)
106. RESULTS
Primary and secondary outcomes: no differences
between groups
Sub-group analyses: no differences
Factors associated with infection risk:
High surgical risk
30 days or younger
Hyperglicemia
Prolonged stay ICU
Post-op glucocorticoid therapy
Not significant when controlling for prolonged ICU
stay
107. INTERNAL VALIDITY:
Threats: convenience sampling, differences in protocol, target population?
Strengths: random allocation, blinding,
No placebo (would be ethical?)
Glucose control in standard care not specified by the protocol
EXTERNAL VALIDITY:
Relative broad inclusion criteria
Sample does no represent all critically ill pediatric patients
Highly trained centers: lower infections and mortality rates anyway