Post-quiz 4 content Flashcards
Compare the purpose of examining internal and external validity.
External → will the results generalize to the population?
Internal → was the outcome due to exposure, or something else?
What are threats to internal validity?
Name 7.
Factors that can interfere with findings from experimental studies.
- History
- Maturation
- Testing
- Selection
- Instrumentation
- Regression to the mean
- Experimental mortality/attrition
What type of study design is this?
Pre-test, post-test quasi experimental study
(i.e., no randomization or controls)
Describe history as a threat to internal validity.
- Specific events that occurred during the study period.
- External factors that influencing outcome that were not part of the intervention.
- E.g., During the intervention, the school cafeteria started serving more fruits and vegetables.
Describe maturation as a threat to internal validity.
- A function of the passage of time between pre-test and post-test (i.e., people change/grow over time)
- E.g., during the intervention, the students got older and became less picky eaters (they started to like fruits and veggies)
Describe effects of testing as a threat to internal validity.
- Pretesting affects performance on later measurements (post-test)
- E.g., After doing the baseline fruit & veg assessment, the students became more aware of the importance of fruits and veggies and started eating ore of them.
What study design should be used if you were concerned about the effects of testing?
Solomon 4-group
Which threats to internal validity can be reduced by using concurrent groups?
History
Maturation
Testing
What notation correctly describes the study?
A
Describe selection as a threat to internal validity.
- Study groups are not comparable/equivalent
- Selection-history
- Selection-maturation
- Selection-testing
- E.g., schools who received the intervention also have free fruit and veg basket that students can pick from; controls did not have this.
How can selection as a threat to internal validity be controlled?
- Random assignment → if randomization is successful, groups should be similar at baseline.
Describe instrumentation as a threat to internal validity.
- Variability in the analysis and evaluation of the outcomes
- Analytical instruments not calibrated or differently calibrated between experiments.
- Two graders scoring pre/post-tests differently
- E.g., FFQ not validated for study population.
- E.g., 2: Raters assessing post study diet after the nutrition intervention overestimated F&V intake
How can instrumentation as a threat to validity be controlled?
By ensuring measuring instruments are reliable.
(e.g., test-retest, parallel forms, inter/intra rater reliability testing → ensure tools are reliable and give same responses each time to minimize error)
Describe regression to the mean as a threat to internal validity.
- If first values measured are extreme, the post-test values may ‘regress to the mean’ simply as a result of day-to-day variation.
- E.g., by ‘chance’ class A scored very low on pre-test (extreme finding). On second testing, their scores moved towards the mean → may conclude class A improved more when this is actually just ‘regression to the mean’
Describe experimental mortality/attrition as a threat to internal validity.
- Loss to follow-up
- A concern if characteristics of dropouts differ from those who remain in the study, or if dropout rates differ between intervention and control group.
What is intention to treat?
‘once randomized, always analyzed’
Participants are included in analysis in the group they were originally assigned to regardless of whether they completed the trial.
What study design best describes the following:
- 8 elementary schools assigned to receive intervention or not (controls)
- Intervention designed to improve diets, increase physical activity, and decrease screen time
- Assessed students’ diets before and after the intervention
Pre-test, post-test, quasi experimental parallel study
At baseline, the groups did not have different fruit and vegetable intakes.
What threat to internal validity exists here?
Selection
What needs to be considered for external validity?
Need to consider how findings from a study can be generalized to the target population in terms of:
- Sample - representative of population?
- Setting - realistic?
- Study conditions - impact results?
How can external validity be increased?
- Random selection of participants from a population → increase representativeness and ability to generalize results
- Account for the research context → specific aspects of the study may limit the generalizability of the results outside the research settings.
What are advantages of randomized controlled trials? [5]
- Controls for possible confounders → aims to have comparable groups by randomization
- Level of exposure controlled/manipulated by researcher
- Control group for comparison (ensure effects are due to treatment)
- If blinded, reduces bias
- Provides evidence about temporality of associations
What are limits to randomized controlled trials?
- Cost
- Feasibility → ethical implications
- Large sample size needed for statistical power
- Poor compliance and drop outs
- External validity/generalizability
What are 5 nutrition RCT challenges?
-
Duration
- Longer interventions → difficult to have compliance with dietary interventions over long term
- Shorter interventions → long enough to have impact?
-
Controlling exposure
- Difficult to completely ‘control’ intake of a nutrient
- Difficult to have good compliance with nutrition interventions
-
Level of exposure
- Cannot have zero intake group of essential nutrient
- Typically comparing ‘some’ intake with ‘more’ → how to define ‘some’ and ‘more’; ‘some’ may already be enough for outcome of interest → threshold effects
-
Nutrients vs. food
- Will supplement of omega-3 fatty acid produce the same effect as obtaining omega-3 fatty acid from eating fish?
-
Difficult to accurately measure nutrient intake
- Rely on memory and subject’s ability to accurately recall foods consumed & portion sizes
- Foods consumed vary meal-to-meal and day-to-day
- Similar foods may vary in nutrient content.
Thinking critically…
Do omega-3 fats actually have no risk on CVD factors? OR… [5]
- Did subjects already have adequate intakes at baseline?
- Was dose provided clinically relevant?
- Were results influenced by the use of concurrent treatments (e.g., statins)
- Are omega-3 fats only beneficial for prevention of primary CVD not secondary CVD?
- Could effects of omega-3 on CVD risk factors (from observational studies) be explained by something else? (e.g., fish intake, vitamin D and protein, etc.)
Review papers are sometimes called:
Secondary research
What is a narrative review?
What is a problem with narrative reviews?
- ‘expert’ in a field writes article that summarizes the evidence
- can reflect the state of the field, be a summary of current/past research on a topic, provide new opinions, suggest new hypotheses or areas for future research.
- Very useful if you have no idea where to start!
- PROBLEM → High risk of bias (the expert selects the studies included in the review and can focus on those that support his/her opinion)
What is a systematic review?
- Summarizes research on a specific question
- Explicit methods are used to (1) search, (2) appraise, and (3) synthesize the literature
- Potential for bias reduced → all articles meeting the inclusion criteria should be considered.
Rank narrative reviews, systematic reviews and meta-analyses, and RCTs in the hierarchy of evidence for clinical decision making.
Systematic reviews and meta-analyses
RCTs
Narrative reviews
Rank narrative reviews, systematic reviews and meta-analyses, and RCTs in the hierarchy of evidence for clinical decision making.
Systematic reviews and meta-analyses
RCTs
Narrative reviews
What are meta-analyses?
- Used statistical analysis to calculate a summary estimate based on the results of published studies.
- Provides an average of the published results, weighted for differences in the quality/size of the studies
- Usually based on systematic reviews.
What are the 8 steps in systematic review methodology?
- Define research question
- Outline eligibility criteria
- Comprehensively search the literature
- Assess studies and determine which to include
- Assemble a comprehensive data set of studies
- Assess quality of studies
- Perform meta-analysis if appropriate
- Answer research question.
How is a research question defined?
PICO
population
intervention
control/comparison
outcome
Discuss outline eligibility criteria for systematic reviews.
- Studies are ‘subjects’
- What types of studies:
- Only RCTs → all study designs?
- Participants → what age/sex/ethnicity/health status?
- Year of publication → any year, last 5 years?
- What outcomes?
Discuss outline eligibility criteria for systematic reviews.
- Studies are ‘subjects’
- What types of studies:
- Only RCTs → all study designs?
- Participants → what age/sex/ethnicity/health status?
- Year of publication → any year, last 5 years?
- What outcomes?
Which of the following strategies would ensure you get the most papers in your search?
Combining MeSH and keywords with OR
How is literature searched comprehensively for systematic reviews?
- Specify search terms clearly
- Conduct search in more than one database
- Search the ‘grey’ literature (abstracts, conference proceedings, unpublished theses, etc) to avoid publication bias
- Studies that detect a significant difference are more likely to be published.
How are relevant articles selected for systematic reviews?
- Many of the retrieved articles will not be relevant:
- Studies using populations or study design differing from eligibility criteria (i.e., animal studies, non RCT)
- Studies that include an additional intervention (i.e., vitamin D and calcium together)
- Studies that do not include a measure of your outcome of interest
- Document reasons for exclusion!
How is a data set assembled comprehensively for systematic reviews?
- Tabulate data from included studies:
- study population characteristics
- sample size
- specific intervention
- duration of follow-up
- outcomes measured
- etc…
How is the quality of included studies assessed for systematic reviews?
- Assessment criteria should be specified
- E.g., randomization, blinding
- Can use a checklist
- ADA checklist to assess research papers
- CONSORT
- At least 2 reviewers should do this independently
How is the quality of included studies assessed for systematic reviews?
- Assessment criteria should be specified
- E.g., randomization, blinding
- Can use a checklist
- ADA checklist to assess research papers
- CONSORT
- At least 2 reviewers should do this independently
Why is meta-analysis conducted?
Combines the results of individual studies to increase the overall sample size → improves the statistical power of the analysis
What are treatment effects considered for meta-analyses?
Determination of the treatment effects for each study.
- Odds ratio (OR)
- Relative risk (RR)
- Mean difference → (mean group 1 - mean group 2)
- 95% confidence interval
When is OR, RR, or mean difference significant?
OR, RR → significant if CI does not cross/include 1
Mean difference → significant if CI does not cross/include 0
How are meta-analyses conducted?
- Determine treatment effect for each study (OR, RR, mean difference, 95% CI)
- Calculate overall treatment effect as a weighted average of individual treatment effects (weighting gives more emphasis to larger individual studies)
- Display data.
How are forest plots interpreted?
- Each ‘black box’ shows the OR (RR or mean diff) for an individual study → the lines extending from the box shows the 95% CI
- The size of the black box reflects the weight of the study in the meta-analysis (and usually, the sample size)
- The clear weighted diamond is the weighted mean of all the studies
Of all the 9 studies in this forest plot, how many showed a statistically significant effect of the treatment?
3
Why is heterogeneity assessed?
Are results from individual studies, in general, consistent?
- Study results may differ due to differences in:
- Characteristics of the participants
- Study design (length of intervention, dose)
- Outcome measurements
- If substantial heterogeneity exists it may not be appropriate to combine studies.
- Analysis may be repeated in subgroups to see if heterogeneity is improved.
How can we test for heterogeneity?
- Look at forest plot, CI should overlap
-
Chi2 (or Cochrane’s Q)
- Are differences between studies due to chance alone?
- If significant (P<0.05), there is heterogeneity between studies
- Are differences between studies due to chance alone?
-
I2
- Percent variation in studies due to heterogeneity
- Generally >50% = substantial heterogeneity
What happens if there is heterogeneity between individual studies in a systematic review? [4]
Don’t do meta-analysis
Remove studies
Sensitivity analysis with subsets of studies
Account for it in a ‘random-effects’ model
How is publication bias assessed?
Funnel plot
How is a Funnel Plot interpreted?
- The vertical axis is a measure of the study size or precision of the study (e.g., standard error)
- The larger and more precise (i.e., less variable) the study, the further up it is placed on the plot
- The horizontal axis measures treatment effect
- An approximately symmetrical distribution of studies on either side of the overall effect suggests low bias
- Un-symmetrical distribution of studies suggests a publication bias.
Why does this un-symmetrical funnel plot suggest publication bias?
It suggests that only studies that confirm the original hypothesis were published.
The overall effect is a RR < 1 (treatment was protective).
Small studies that disagreed with this were not published. (i.e., studies that showed a harmful treatment effect were not published)
This may be all of the research out there → limitation of Funnel plots
What are advantages of systematic reviews? [3]
- Summarizes current research
- Systematic methods for data retrieval limits potential for bias
What are advantages of systematic reviews? [3]
- Summarizes current research
- Systematic methods for data retrieval limits potential for bias
- Considered to be evidence of the highest level in the hierarchy of research designs.
What are limitations of systematic reviews? [4]
- Limited by publication bias
- Differences in methods for selecting and assessing quality of papers that may affect results
- Averages may miss effects in certain groups
- Systematic reviews may not always be updated → to ensure information is up to date:
- Check publication date
- Look for new papers published after that date
→ Results from systematic reviews and meta-analyses still need to be interpreted critically.
Why are systematic reviews (and meta-analyses) at the top of the evidence hierarchy?
- By combining studies they achieve a larger sample size that has more power to detect a significant difference.
- Specific search and study eligibility criteria reduce bias
What is the Cochrane Database of Systematic reviews? [3]
- A Cochrane Review is a systematic review of research in health care and health policy
- Follow specific protocols for searching, assessment and compiling data
- Updated every ~2 years unless there is no new information.
Why use PEN?
Dieticians are expected to provide professional, safe, ethical, and competent practice to their clients → keeping current!
PEN database can help address barriers to using research in practice.
Barrier → exponential growth of health-care research (knowledge) that is not being translated
Facilitator → PEN database helps you access evidence-based practice guideline, tools, and resources for every day food and nutrition questions.
What does the PEN system provide?
Provides nutrition practitioners with ready access to timely, current, and authoritative guidance on food and nutrition. It offers evidence-based answers to the questions encountered in every day practice.
How is the PEN system useful for students?
- Learn about basic nutrition knowledge
- Support assignments
- Learn how literature is critically appraised to support practice
- Prepare for case studies or patient simulations
How is PEN useful for practitioners?
- Keep on top of the evidence
- Respond to clients and interests and needs
- Access professional tools, resources, and handouts
- Be part of the PEN global community.
What is the primary difference between experimental and observational studies?
The investigator controls the subject’s exposure in an experimental study, but not in an observational study.
In a research article, where would you find the purpose of the study described?
introduction.
Why are animal studies at the bottom of the hierarchy of evidence for making clinical decisions?
Findings from animals cannot directly translate to human physiology as animal are not humans.
What type of study does this abstract describe?
Systematic review, which are generally considered a strong level of evidence (i.e., they are high on the hierarchy of evidence for clinical decision making)
What type of research is described in the following study?
Quantitative descriptive.
What type of study does this abstract describe?
Experimental
A researcher is interested in determining whether higher intake of iodine is associated with lower risk of thyroid cancer (a rare disease).
The most feasible study design to address this would be:
Case control study
What is the C in this PICO question:
Among individuals with type 2 diabetes, is a low carb diet, compared to a standard diet, associated with improved glucose control?
Standard diet.
Medline is a platform that is used to search OVID.
True or False?
False.
Medline is more reliable than PubMed for searching the literature.
True or False?
False.
OVID is a platform that is used to search Medline.
True or False?
True.
Google Scholar is not a reliable way to find scientific articles.
True or False?
False.
Kyle has done a literature search and retrieved 1500 abstracts. What is a good strategy to refine his search while still keeping relevant articles?
Apply limits at the end of his search.
What would the most comprehensive search for a topic in Medline include?
MeSH terms and keywords combined with ‘OR’
A researcher is studying the relationship between omega-3 fatty acids, and blood pressure. They find a weak inverse association between omega-3 fatty acids and blood pressure in their sample as a whole; however, in further analysis, they find that the association is stronger among people who are obese, and weaker in those who are not obese.
What is obesity in this example?
An effect modifier.
One of the issues when trying to find a dose-response relationship in nutrition is that nutrient-outcome relationships […].
Generally do not have linear relationships
Karimah is interested in studying whether higher folate intake decreases homocysteine levels (a marker of CVD). She finds 10 studies that show a relationship between higher folate and lower homocysteine and all suggest that taking a folic acid supplement can decrease homocysteine levels by >20%.
Which criteria of causation do these findings meet?
Strength of association
Consistency
In a hypothetical study, elderly subjects were given a vitamin D supplement or placebo for 5 years to determine whether vitamin D supplements decrease the risk of falls or fractures. At the midway point of the study (2.5 years in), the interim analysis revealed that vitamin D supplements were associated with a clinically significant reduction in hip fractures. The researchers decided to continue the study to the end to see if this changed over time.
What main ethical principle was violated when the researchers did not offer the placebo group a vitamin D supplement even though it was shown to have beneficial health effects?
Concern for welfare
Joe wants to study the impact of daily exercise therapy in individuals with advanced Alzheimer’s disease.
What would Joe have to do to ensure his study follows ethical principles for consent in this case?
Ensure that the benefits of the study outweigh the potential risks.
The university REB approves all university-affiliated research studies involving human participants.
True or False?
True.
The REB is comprised of six community members with no expertise or vested interest in the research.
True or False?
False
The REB must include at least one representative from the tri-council.
True or False?
False.
The REB decides how research funds are distributed.
True or False?
False.
A TA insists their students sign up for his study.
Is consent ‘free’ in this case?
No
A doctor tells his patient that they must sign up for a research study in order to get the best care.
Is consent ‘free’ in this case?
No
Cord blood is taken from a baby at birth and used for a research study without the parent’s knowledge.
Is consent ‘free’ in this case?
No.
Before signing a consent form, participants are informed of the benefits and risks of the study and are told that they will be offered a $100 gift card in exchange for participating.
Is consent ‘free’ in this case?
Yes
The Canadian Council on Animal Care sets ethical standards for use of animals in both research and teaching.
True or False?
True
The Canadian Council on Animal Care approves animal study ethics and protocols applications.
True or False?
False.
The Canadian Council on Animal Care approves animal study ethics and protocols applications.
True or False?
False.
The Canadian Council on Animal Care is a member of the tri-council of Canada.
True or False?
False.
The Canadian Council on Animal Care provides training for those who work with animals in research.
True or False?
False.
Benny is studying the effects of fish oil on early brain development using a mouse model.
From previous work, Benny believes he will need at least 8 animals per group to see a significant effect of diet; however, in his protocol, Benny states that he will need at least 20 animals in each diet group to ensure that he has enough samples in case he wants to do any additional tests.
Benny is not following the principle of […].
Reduction
Joelle is studying the impact of maternal diet on offspring birthweight using a mouse model.
Why are mice an appropriate model here?
Because mice have a short gestation time.
What is a major concern with using genetic variant mouse models in research?
The variant may have broad effects on the health of the organism that could confound research findings.
Why are focus groups used in qualitative research?
To see where participants agree or disagree
What is the main difference between qualitative and quantitative research?
Qualitative research aims to explore human behaviours in specific contexts, whereas quantitative research aims to find relationships that can be generalized to populations.
What does reflexivity in qualitative research refer to?
Recognizing the role of the researcher in influencing data collection and analysis.
Jane designs a survey to look at breakfast consumption and academic performance in UBC students. The survey has 20 questions that ask students about their breakfast eating habits and a final question that asks students to self-report their GPA. The breakfast portion of the survey has been previously validated in another study, and had a test-retest ICC of 0.8. She sends the survey to 2000 students and gets 200 responses.
When reading her findings, are you concerned about any of the following:
- non-response bias
- interviewer bias
- misreporting
- unclear questions
- survey is not valid or reliable
Non-response bias
Misreporting
In a study on parent choices for student lunches, parents were asked to complete a survey asking about how many servings of each food group they typically pack in their child’s lunch, and then they were invited to an interview to discuss what influences their choices.
What type of study is this?
Mixed methods
What is a benefit of open-ended surveys?
Allows participants to provide answers that may not be included in a closed-ended question.
Rachelle developed a survey to assess people’s adherence to the guidelines in Canada’s Food Guide. Her survey included 25 questions that asked participants to agree or disagree with statements on a Likert scale.
In development, Rachelle noted that the survey had good face and criterion validity, and a Cronbach’s alpha of 0.4.
Rachelle wants to add up the scores from the survey to develop a Canada Food Guide compliance rating system and asks for your advice on whether this is appropriate. What advice would you provide to Rachel about her proposed compliance rating?
She should not add up the scores from her scale because the items do not address the same underlying construct.
In a study of micronutrient supplements, researchers randomly assigned half of the participants to receive a B vitamin supplement and the other half received a placebo. B vitamins, in particular riboflavin, taken at high doses can alter the color of urine. To control for this, the placebo also contained a compound that colors urine.
Why was this done?
To ensure blinding
To determine whether a new hospital menu plan would decrease the length of hospital stays, researchers randomly selected 10 hospitals in BC and then randomly assigned the hospitals to either receive the new menu plan or continue with their current meal service for six months. The length of hospital stay was compared between patients who received the new meal plan and those who did not.
What type of study design is this?
Quasi experimental
To determine if fibre intake is a risk factor for development of type 2 diabetes, researchers assessed fibre intake of 500 women at enrollment using a food frequency questionnaire, they then followed the participants for the next 20 years and recorded any incident cases of type 2 diabetes.
What type of study design is this?
Prospective cohort
A large study was designed to determine whether regular use of antioxidant supplements reduces the risk of cognitive decline. Participants were asked to report their use of supplements and then were followed for 20 years. 10 years into the study, the researchers noticed that a number of participants have reported hip fractures. They decided to investigate this further by selecting 100 people from the study who had hip fractures and 100 who did not report a hip fracture and compare whether nutrient intake differed between these two groups.
What type of study is this?
Nested case control
In prospective cohort studies, recall bias may lead to differential misclassification of dietary intake.
True or False?
False.
A hypothetical study followed 1000 people who graduated with a nutrition degree and another 1000 university graduates who did not receive a nutrition degree. After 35 years, the study found that 100 of the subjects who graduated with a nutrition degree had developed cardiovascular disease. The relative risk of developing cardiovascular disease in subjects who had a nutrition degree compared to those who did not have a nutrition degree was 0.50 .
Based on this, subjects who graduated with a nutrition degree were 50% as likely to get CVD as subjects who did not graduate with a nutrition degree.
True or False?
True
A hypothetical study followed 1000 people who graduated with a nutrition degree and another 1000 university graduates who did not receive a nutrition degree. After 35 years, the study found that 100 of the subjects who graduated with a nutrition degree had developed cardiovascular disease. The relative risk of developing cardiovascular disease in subjects who had a nutrition degree compared to those who did not have a nutrition degree was 0.50 .
Based on this, the absolute risk of developing CVD among nutrition graduates was 10%.
True or False?
True
A hypothetical study followed 1000 people who graduated with a nutrition degree and another 1000 university graduates who did not receive a nutrition degree. After 35 years, the study found that 100 of the subjects who graduated with a nutrition degree had developed cardiovascular disease. The relative risk of developing cardiovascular disease in subjects who had a nutrition degree compared to those who did not have a nutrition degree was 0.50 .
Based on this, the absolute risk reduction for CVD associated with having a nutrition degree (compared to not having a nutrition degree) was 50%.
True or False?
False.
A hypothetical study followed 1000 people who graduated with a nutrition degree and another 1000 university graduates who did not receive a nutrition degree. After 35 years, the study found that 100 of the subjects who graduated with a nutrition degree had developed cardiovascular disease. The relative risk of developing cardiovascular disease in subjects who had a nutrition degree compared to those who did not have a nutrition degree was 0.50 .
Based on this, the absolute risk of developing CVD among subjects without a nutrition degree was 20%.
True or False?
True
In a study to assess knowledge about the Canadian Food Guide before and after an educational intervention, a pre-test post-test design would be recommended.
True or False?
False.
In a study to assess whether folate levels increase after consuming spinach, a pre-test post-test design would be recommended.
True or False?
True.
A case-control study was designed to investigate the association between hypertension and fruit and vegetable intake. The odds ratio for fruit and vegetable intake among cases compared to controls was 0.70 (95% CI 0.30, 1.1).
This should be interpreted as:
Subjects with hypertension were less likely to consume fruits and vegetables than controls, but this finding was not statistically significant.
Researchers aimed to investigate whether vitamin C reduces the risk of COVID 19.
They invited 2000 randomly selected people from British Columbia to participate in the study. Of these, 200 agreed to participate. Those who agreed completed a food frequency questionnaire to assess vitamin C intakes and were asked to inform the researchers if they tested positive for COVID 19 over the next three years.
At the end of three years, the researchers had a final sample size of 192 and found that vitamin C intake was not associated with risk of COVID 19.
What is a limitation of this study?
The study may not be representative of the population because of its low response rate.
Which is true?
- RR of breast cancer was not significantly different from 1.00 across any of the quintiles of multivitamin intake.
- Subjects in quintile 4 were less likely to develop breast cancer than subjects in quintile 1 and this finding was statistically significant
- Subjects in quintile 4 and 5 were less likely to develop cancer than subjects in quintile 1 and these findings were statistically significant.
- Subjects in quintile 2 were less likely to develop breast cancer than subjects in quintile 1, but this finding was not statistically significant
- Subjects in quintile 4 were less likely to develop breast cancer than subjects in quintile 2 and this finding was statistically significant.
Subjects in quintile 4 were less likely to develop breast cancer than subjects in quintile 1 and this finding was statistically significant
Recognizing that many nutrition studies use supplement doses that are much higher than what would be obtained from foods, a researcher designed a study in which participants were randomly assigned to receive a low dose vitamin C supplement or placebo for three months. The dose of vitamin C given was comparable to what people would get from food if they were consuming a diet according to Canada’s Food Guide.
The researchers then assessed whether taking the low dose supplement was associated with decreased incidence of common colds.
A problem with this study is that:
Vitamin C intakes of the two groups may overlap
A case-control study aimed to investigate the relationship between red meat consumption and cancer. The study included 160 cases with cancer and 609 control subjects. Each participant was classified as consuming red meat > 4 times per week (exposed) or ≤ 4 times per week (unexposed).
The results were as follows: 56 cases ate red meat > 4 times per week and 104 cases ate red meat ≤4 times per week; whereas 109 controls ate red meat > 4 times per week. What is the odds ratio for eating red meat > 4 times per week among cases compared to controls?
2.47
To determine whether fish or omega-3 fatty acid intake is associated with reduced risk for depression, researchers enrolled 2000 females with diagnosed depression and 2000 females who had not been diagnosed with depression and asked each to complete a survey asking about their food and supplement intake over the previous two years.
The researchers determined whether fish or omega-3 fatty acid intake was associated with depression by calculating an odds ratio.
A main concern you would have with this study is that:
Temporality cannot be established.
Which of the following research questions is best suited with a cross-over design?
- Does regular use of omega-3 supplements decrease pain in labour?
- Does consumption of vitamin C improve zinc absorption?
- Is a course on basic nutrition knowledge effective in improving glucose control?
- Are dietary essential fatty acids protective against cancer?
Does consumption of vitamin C improve zinc absorption?
How can history & maturation as a threat to internal validity be reduced?
The use of a control group, selected from the same population as the experimental group and which experiences the same concurrent history as the experimental group.
Also, the shorter the duration of an experiment, the less likely history and maturation will be a threat.
How can testing as a threat to internal validity be reduced?
The use of a research design that does not include pre-test.
Use different but equivalent forms of a test for pre-test and post-test.
The use of a no-treatment control group may help to rule out the effects of testing.
How may instrumentation as a threat to internal validity be reduced?
Careful specification and control of the measurement procedures can eliminate most instrumentation threat.
Standardized instruments, administration or data collection procedures, and the training of study personnel are among the methods that help control this threat.
How may statistical regression to the mean as a threat to internal validity be minimized?
Avoid assigning subjects to groups based on their extreme scores.
How may attrition as a threat to internal validity be minimized?
Recruit large groups of participants or more than needed for statistical analyses.
Include incentives and compensation as appropriate.
How may selection as a threat to internal validity be reduced?
Random selection (sampling) and random assignment of subjects to groups.
If random selection and assignment are not possible, then use of certain statistical techniques (e.g., ANOVA) that can adjust for group differences.
What are some limitations of cross-sectional studies?
Limitations: Non-response bias; misreporting, cannot show disease incidence or temporality
