Revision For Quiz 1 - Epi

Prevalence

What proportion of the population actually has the disease at a specific time point.

Point Prevalence

What proportion of the population has the diseases at a specific time point.

Lifetime Prevalence

What proportion of the population had the diseases at some point in life.

Period Prevalence

What proportion of the population has the diseases at any point during a given time period.

Incidence

What proportion of the population newly acquired the diseases during a given time period.

Incidence Proportion (IP) or Cumulative Incidence or Attack Rate

the proportion of people who develop the disease or become injured or die or are at risk of getting the disease during a given time period (cross-sectional).

Incidence Rate (IR)

The proportion of people who develop the disease or cure or becomes injured or dies or is at risk of getting the disease per unit of time (longitudinal).

What happens to prevalence if there is an increase in incidence?

There is an increase in prevalence.

What happens to the cure rate if the death rate is increased?

The cure rate decreases.

Crude Mortality Rate

The mortality rate from all causes of death for a population.

How do you calculate crude mortality rate?

The total number of people that have died during a given time period/ total number of the population in the same time period (reported in 1000 or 100,000).

Cause Specific Mortality Rte

The mortality rate from a specific cause for a population in the same time period.

How do you calculate cause specific mortality rate?

The total number of people that have died during a given time period from a specific cause/ total number of population in the same time period (reporter in 1000 or 100,000).

Proportional Mortality Rate

The proportion of deaths in a specified population during a given time period attributable to different causes.

How do you calculate proportional mortality rate?

The total number of people that have died due to a specific cause during a given time period/ Total number of people that have died from all causes during the same time period.

Death to Case Ratio

The total number of people that have died due to a specific cause during a given time period / total number of new cases reported for that specific cause in the same time period.

Infant Mortality Rate

The total number of infants under 1 year of age that have died during a given time period/ total number of live births reported during the same period.

Maternal Mortality Rate

Total Number of deaths of women during pregnancy, during childbirth, or within 42 days of termination of pregnancy during a given time period/ Total number of live births reported during the same time period (reported in 100,000).

What do standardised rates do?

Helps to compare morbidity and mortality between two or more populations.

Why is the comparison of crude mortality and morbidity often misleading?

Because the populations underlying characteristics may differ, such as age or gender.

Standardisation rates

A method for overcoming the effect of few confounding variables commonly age and gender

Direct method of standardisation rates

Comparing sampled population to a reference population. Useful with large sampled population.

Indirect method of standardisation rates

Used when reference population data is not available. Used when the sampled population is very small and comparison to reference population can produce incorrect findings.

What are the practical implications of standardisation population based morbidity and mortality indicators?

The usefulness of standardised rates, as the terminology suggests, are the standardised rates, therefore, can help to compare data across ecological data sets. It helps to interpret research data accurately.

Life Expectancy

The average period that a person may expect to live.

Healthy Years OR Disability-free Life Expectancy

The number of years that a person is expected to continue to live in a healthy condition.

Years of Lost Life (YLL)

The number of years of life lost due to premature death, defined as dying before the ideal life span.

Disability-adjusted Life Years (DALY)

A measure of healthy life lost, either through premature death or living with disability due to illness or injury.

Population Based: Descriptive Studies

Provides distribution (percentages, frequencies) of diseases. Does not provide causes of disease.

What are the strength of population based descriptive studies?

They are quick and easy and useful for identifying variations in the distribution of disease or in the distribution of factors.

What are the limitations of population based descriptive studies?

Limited ability to identify associations- cause-effect relationship.

Population Based: Ecological Studies

An observational study defined by the level at which data are analysed, namely at the population or group level, rather than an individual level.

What are the strength of population based ecological studies?

Quick and easy if using secondary data, Useful information about various factors associated with a condition , Useful for forming hypotheses about diet/disease relationship .

What are the limitations of population based ecological studies?

May not be applicable at an individual level, No cause-effect relationship.

Case Report/Case series studies

A particular case in a patient, population/sample group discusses.

Cross-Sectional studies

The association between exposure variable and outcomes identified.

Case-Control studies

Comparing an interest group to a reference group (no randomisation).

Strengths for Individual Based Studies

Relatively quick and inexpensive , Can investigate a wide variety of potential risk factors simultaneously , Can be applied to common and rare diseases.

Limitations for Individual Based Studies

Retrospective design, Subject to several types of bias, No cause-effect associations

Cohort/prospective/longitudinal/retrospective study

A sample followed by x amount of time. For example, a 10 years longitudinal study showed that low F&V intake is related to cancer.

Strengths of cohort studies

Information is more reliable and applicable to normal life- participants followed in daily conditions. Allow determination of the timing of events.

Limitations of cohort studies

Time-consuming and expensive, Changes in behaviour may mislead results , High potential for selection bias and confounding factors , Drop out rates, generalisation of the findings, No cause-effect associations.

What is an example of a one-shot case study design?

A researcher wants to study the effect of a reading program on reading achievement.

She might implement the reading program with a group of students at the beginning of the school year and measure their achievement at the end of the year.

What is an example of a pretest-posttest case study design?

We also do not know whether the students' reading skills actually changed from the start to end of the school year.

We would improve on this design by giving a pretest at the start of the study.

Researchers recruit subjects than randomly assign them to receive or not receive a treatment under investigation, Observe to see whether intervention influences occurrence of disease Ideally should be:

• Randomised

• Placebo controlled (preferably double-blind)

• Cross-over design

Community Intervention RCT

Intervention trial carried out at the community level (C-RCT)

Experimental/Intervention Studies Strengths

Tightly controlled, Can provide direct evidence of cause and effect (RCT only).

Experimental/Intervention Studies Weaknesses

Limited application (ethical issues), Subject compliance , Need long-term intervention to detect an effect - cost prohibitive , Can assess only 1 or 2 factors at a time.

Original Research

Review Articles

Summarise the findings of other studies or experiments; attempts to identify trends or draw broader conclusions. ( A valuable source to find more references in your related area; the content is generally used in writing your literature review and discussion).

Meta-Analysis

This type of research article also summarises the findings of others studies or experiments, however statistical analysis is conducted to derive conclusions. Therefore, a review is a narrative, whereas a meta-analysis has a narration along with numerical conclusions.

Case Study

useful for clinical based research. They describe a single case or a similar trend observed. For example, diabetic nephropathy observed in Alzheimer’s patients in a particular hospital.

Letter to the editor or short communications

They may describe an original research very briefly, They may respond to a previously published research article, if they have a difference of opinion , They could reply to the authors who had a difference of opinion.

Government documents/reports

usually sourced directly from google

Rate Ratio or Incidence Density Ratio

Rate ratio levels

1 is equal rates in the two groups, >1 indicates increased risk in exposed groups, <1 indicates decreased risk in exposed groups.

A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or deaths) among one group with the risk among another group.

Risk ratio equation

IRe/IRu (from both groups)

Difference in the Definition of Rate Ratio and Risk Ratio

Rate Ratio is when the ratio of the rate of an event in one group (exposure or intervention) to that in another group (control) & Risk ratio is the ratio of the risk of an event in one group (exposure or intervention) to that in another group (control).

Attributable Risk

AR is the difference between the incidence of disease in the exposed population versus incidence in the unexposed population.

Attributable Fractions (AFs)

AFs = (IRe-IRu)/IRe

Odds Ratio

The ratio of the odds of an event occurring in the exposed group versus the unexposed group

Validity

Criterion Validity

Whether the instrument/procedure is measuring what it should measure. Eg, an IQ test should measure IQ.

Face Validity

The degree to which the purpose of the instrument/procedure is clearly understood to the participants.

Content Validity

Validity of a construct

Convergent Validity

examines whether data obtained from two different procedures/instruments measure the same construct.

Divergent Validity

examines whether the construct of interest is different from other constructs present in a research.

Internal Validity

The confidence that the independent variable has only caused the outcome/dependent variable. Therefore, control for confounders.

External Validity

The validity of generalisation.

Reliability

The consistency in the measurement, precision

Measures the variation in the measurements taken by the same person or using the same instrument on the same item and under the same conditions.

Two or more trained researchers record observations of the subjects independently.

Overall Reliability or Internal Consistency

It examines whether the items proposed to form a construct/scale measures what it is intended to measure.

Type I error

H0 is true, but results show significance.

TypeII error

Reject H0, but it is not significant.

Null Hypothesis (H0)

There is no association between IV and DV. Null hypothesis accepted.

Alternative Hypothesis (HA)

There is an association between IV and DV. Null hypothesis rejected.

p-values

Significance of 0.05 reflects that there is a 95% confirmation that your results are accurate and not occurred by chance.

An effect size is a standardised measure. Results from different studies can be compared based on the effect size.

Difference Between Significance and Effect Size

Significance reflects that there is 95% confirmation that your result has not occurred by chance, Effect size reflects the strength of the model.

Biological Variation

Fluctuation in biological processes in the same individual over time

Sampling Error

Error caused by random influences on who is selected for the study

Measurement Error

The error resulting from random fluctuations in measurement.

Poor study design and unclear aims and methods. To address it, clearly define risk and outcome, preferably with objective or validated methods. Standardised and blind data collection.

Confounding bias

Withdrawal rate; age; sex. To address, control confounders.

Channelling bias

Type of allocation bias. When participants with specific illness/health are allocated to a specific group for favourable results. To address, clearly define risk and outcome, preferably with objective or validated methods. Standardise and blind data collection.

Measurement Bias

Occurs if a tool or instrument has not been assessed for its validity or reliability. To address, use reliable and valid tools.

Interviewer bias

To address, standardize interviewers' interaction with patients. Blind interviewer to exposure status.

Hawthorne effect or social desirability bias

Participants respond differently because they are being studied. To address, data collection by middle-person, participants ensure data confidentiality, non-judgemental, benefiting larger causes.

Chronological bias

Time as a potential confounder, participants recruited during Christmas vs those recruited in January. To address, participants recruited during the same timeframe, control during analysis.

Participant Recall bias

To address, use objective data sources whenever possible. When using subjective data sources, corroborate with medical records.

Transfer bias

Participants lost to follow-up. To address, plan for follow up loss by convenient office hours, personalized patient contact via phone or email, home visit.

Exposure misclassifications

Eg FFQ only capturing intake of F&V cannot be generalised to an overall healthy diet. To avoid, clearly define exposure prior to study. Avoid using proxies of exposure. Use validated measures.

Outcome misclassifications

Eg BMI used as an indicator of adiposity. To address, same as exposure misclassifications.

Performance bias

Knowledge of interventions allocation, in either the researcher or the participant. To avoid, double-blind designs, C-RCT.

Analysis bias

Eg reporting only significant findings or findings supporting hypotheses. To address, report results ethically.

Citation/Publication bias

studies are more likely to be published if reporting statistically significant findings. Industry-funded results publishing findings only if it supports their product. To address, during the planning stage discuss MOU/collaborative agreements/intellectual property agreements.