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Terminology. Scientific Epidemiological Statistical . Scientific terminology. Empirical Fact Obvious observation from experiment Empirical observation – a process of gathering information by direct observation

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Terminology

Scientific

Epidemiological

Statistical


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Scientific terminology

  • Empirical Fact

    • Obvious observation from experiment

  • Empirical observation – a process of gathering information by direct observation

    • Evidence is said to be empirical if it is based on observations and measurements of reality

Evidence-based Chiropractic


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Terminology (cont.)

  • Empirical research is:

    • Research which is based on observed and measured phenomena and

    • Is research that derives knowledge from actual experience rather than from theory or belief

Evidence-based Chiropractic


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Terminology (cont.)

  • Assumption

    • A fact or statement taken for granted

    • Accepted as true based on logic, without proof

  • Hypothesis

    • An educated prediction of the outcome of an experiment

Evidence-based Chiropractic


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Terminology (cont.)

  • Law

    • Principles that are taken to be universally applicable

      • Newton’s laws of motion

      • Boyle’s law

    • A statement of fact detailing a sequence or relation of phenomena that is invariable under given conditions (Stedman’s Medical Dictionary)

Evidence-based Chiropractic


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Terminology (cont.)

  • Theory

    • An explanation for some phenomenon which is based on observation, experimentation, and reasoning

    • Hypothesis that is well confirmed or established

  • Cause

    • Something that makes an event happen

    • Science is often interested in looking at cause-effect relationships

Evidence-based Chiropractic


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Theory vs. hypothesis

  • A theory is an explanation

    • The validity of a theory depends on its ability to explain phenomena

    • Theories may be supported, rejected, or modified based on new evidence

  • A hypothesis is a testable idea

    • Scientists do not set out to “prove” hypotheses, but to test them

    • Often multiple hypotheses are posed to explain phenomena; the goal of research is to eliminate those that are incorrect

Evidence-based Chiropractic


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Terminology (cont.)

  • Objectivity

    • Scientists are responsible for putting aside their biases and beliefs and seeing the world as it “really is”

    • No one is ever perfectly objective

    • Some scientists are less objective than others, which is one reason we have to critically evaluate research

Evidence-based Chiropractic


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Scientific method

  • The principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation . . .

    The American Heritage dictionary of the English language. 4th ed. 2000, Boston: Houghton Mifflin. xxxvii, 2074 p.

Evidence-based Chiropractic


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Scientific method cont.

  • Generally involving:

    • The observation of phenomena

    • The formulation of a hypothesis concerning the phenomena

    • Experimentation to demonstrate the truth or falseness of the hypothesis

    • A conclusion that validates or modifies the hypothesis

Evidence-based Chiropractic


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Cause as risk factor

  • A cause is a factor (or member of a set of factors) which results in a sequence of events that eventually result in an outcome

    Exposure  Outcome

    Cause  Effect

Evidence-based Chiropractic


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Causation

  • Causation is investigated by determining an association between exposure and outcome

    • e.g., Smoking and lung cancer or Chiropractic care and optimal health

  • Study of causation leads to inference

    • From statistical sample data to generalizations (to a target population) usually with calculated degrees of certainty (95%)

Evidence-based Chiropractic


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Establishing cause

Temporal Precedence

then

Cause

Effect

Time

Why this is important

Cyclical Functions

Pain levels

Time

Evidence-based Chiropractic


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Theory

  • A reasoned explanation of known facts or phenomena that serves as a basis of investigation by which to seek the truthStedman’s

Evidence-based Chiropractic


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The building blocks of Theory

  • Concepts

    • Conceptual definitionsare abstract

    • Ideas for research

  • Operational definitions

    • Operational definitions are concrete

    • Deduced from conceptual definitions

  • Propositions

    • Statements of relationships among concepts

Evidence-based Chiropractic


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Concepts

  • Abstractions that allow classification of observations

  • When scalar values can be assigned, they may become variables

  • Variables must be operationallydefined

Evidence-based Chiropractic


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Operational definitions

  • Description and explanation of the exact procedures for measuring or observing the phenomenon, event, or behavior

Evidence-based Chiropractic


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Propositions

  • Propositions state the nature of the relationship between variables (concepts)

  • Hypotheses are derived from propositions

    • An hypothesis is a statement about the expected relationship between two or more concepts that is based on a theory and that can be tested

Evidence-based Chiropractic


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Chiropractic Concepts

  • Variables:

    • Adjustment

    • Subluxation

    • Health

Evidence-based Chiropractic


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Chiropractic Propositions

  • Between subluxation and health

    Subluxation Health

  • Between adjustment andsubluxation

    Adjustment Subluxation

  • Between adjustment and health

    Adjustment Health

Evidence-based Chiropractic


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Epidemiology

  • Epidemiology

    • The science concerned with the patterns of disease frequency in human populations

    • Distribution of disease by person, place, time

  • Assumptions:

    • Disease does not occur randomly

    • Disease has identifiable causes which can be altered and thus prevent it from developing

Evidence-based Chiropractic


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DefinitionofEpidemiology

  • The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. Dictionary of Epidemiology

Evidence-based Chiropractic


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Dr. John Snow the father of epidemiology

  • Dr. Snow lived in London during a severe cholera epidemic

  • The medical establishment thought cholera was spread by miasmas (bad air from decayed organic matter)

  • But Dr. Snow theorized that it was spread by contaminated water

Evidence-based Chiropractic


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The father of epidemiology (cont.)

  • He surveyed the houses near a certain public water pump and discovered that nearly all persons who died had consumed water from that pump

  • He presented his data to the local authorities who immediately had the pump handle removed

  • The outbreak quickly subsided as a result

Evidence-based Chiropractic


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The father of epidemiology (cont.)

  • His theory continued to be rejected by his peers until Vibrio cholerae was eventually identified as the cause of the disease

  • However, the statistical and mapping methods used during the investigation formed the foundation of epidemiology

Evidence-based Chiropractic


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Dr. Snow’s map

Evidence-based Chiropractic


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Close-up of

Dr. Snow’s map

Broad street pump

Deaths

Evidence-based Chiropractic


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Measurement of disease frequency and occurrence

  • Incidence

    • The probability of a person being diagnosed with a disease during a specific period of time (typically one year)

    • The number of newly diagnosed cases of a disease during a specified time period

Evidence-based Chiropractic


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Incidence (cont.)

  • For example, a study of 1,000 bus drivers found 50 new cases of low back pain in one year

    • The incidence is 50/1,000 = 0.05 or 5,000 per 100,000

    • Some workers may have had more than 1 episode of low back pain during the year, but only the first occurrence is usually counted

Evidence-based Chiropractic


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Risk

  • An estimate of the proportion of unaffected persons in a population who will develop the disease of interest over a specified period of time

  • Estimated by observing a population that is at risk over a defined period of time to determine the number of new cases as compared with the total number of persons

Evidence-based Chiropractic


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Prevalence

  • The proportion of persons in a given population that have a disease at a certain point in time

    • The total number of cases of the disease in that population

    • It does not matter when they were diagnosed with the condition

Evidence-based Chiropractic


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Prevalence (cont.)

  • For example, a study of community with a population of 30,000 which found 1,000 persons with migraine headaches

    • The prevalence is 1,000/30,000 = 0.033 or 3,300 per 100,000 persons

    • It doesn’t matter that 200 of the cases were newly diagnosed and 800 already had migraine headaches when the study began

Evidence-based Chiropractic


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Point prevalence

  • The proportion of a population with a disease at a given point in time

    • May underestimate the frequency of certain conditions

Evidence-based Chiropractic


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Period prevalence

  • The proportion of a population that has a disease within a defined period of time

    • Involves repeated monitoring of a population

    • Thus is a better depiction of the overall frequency of a disease

Evidence-based Chiropractic


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Incidence and prevalence

  • Sometimes reported as a percentage

  • For example

    • Manchikanti et al studied 500 consecutive chronic spine pain patients and reported the prevalence of facet joint pain as 55% in the cervical, 42% in the thoracic, and 31% in the lumbar spine

Evidence-based Chiropractic


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Incidence and prevalence (cont.)

  • Prevalence is usually much lower than incidence in short duration diseases (e.g., the common cold)

    • Many people contract colds each year, but relatively few people have a cold at one time because the duration is so short

Evidence-based Chiropractic


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Incidence and prevalence (cont.)

  • Prevalence in chronic conditions is higher than its incidence (e.g., diabetes)

    • There are 1.2 million new cases of diabetes each year, but once diagnosed, the condition remains and each year’s incidence is added to the overall prevalence, minus those who die having the condition = 18.2 million

Evidence-based Chiropractic


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Prevalence and incidence illustrated

Evidence-based Chiropractic


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Case begins

Case ends

Evidence-based Chiropractic


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Causation in epidemiology

  • In order to determine whether exposure to a specific risk factor actually caused a particular disease within a population, three key criteria should be met

    • Temporality

    • Consistency

    • Dose-response

Evidence-based Chiropractic


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Temporalitya.k.a., temporal precedence

  • The exposure must occur prior to the onset of a disease

  • However, just because a given exposure precedes a given disease, does not necessarily mean there is a cause-and-effect relationship

  • Alternate explanations are possible

Evidence-based Chiropractic


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Temporality (cont.)

  • Four possible interpretations of temporal relationships

    • Event A caused event B

    • Event B caused event A

    • Both events A and B were caused by a third related event

    • Neither A or B are related to each other or a third event, but the temporal relationship was merely by chance

Evidence-based Chiropractic


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Consistency

  • Studies on the relationship carried out by other researchers using different populations get similar results

  • A large number of good quality observational studies reporting consistent results are required in order to conclude that A caused B

Evidence-based Chiropractic


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Dose-response

  • When greater exposure to a risk factor results in a greater effect on health

  • For example, the more cigarettes a person smokes per day (the dose), the more likely they are to develop lung cancer (the response)

Evidence-based Chiropractic


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Bradford Hill’s criteria for causation

  • Six additional criteria used to identify cause-and-effect relationships

  • Keep in mind, none of these criteria can bring indisputable evidence for or against a cause and effect relationship

Evidence-based Chiropractic


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Bradford Hill’s Criteria of Causation

  • Strength of association – The stronger the relation between the risk and the outcome is, the less likely it was caused by other factors

  • Consistency – The replication of study results by different researchers in a different setting

  • Specificity in the cause – The exposure should be associated with a single specific disease

  • Temporality – The exposure must precede the disease

  • Dose response relationship – Increased exposures should correspond to increased risk of disease

  • Plausibility – There should be a rational scientific basis for the association risk of disease

  • Coherence – The association must be consistent with other knowledge on the topic

  • Experimental evidence – Research that is based on experiments reinforces a causal inference

  • Analogy – The association is analogous to a known causal relationship

Evidence-based Chiropractic


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Bradford Hill Criteria (cont.)

  • Were developed for use in the field of occupational medicine, but  have been widely applied in other fields

  • Criteria serve as a general guide, and are not meant to be an inflexible list

  • Findings of experimental research is preferred, but oftentimes research questions and variables do not lend themselves to rigorous investigation

Evidence-based Chiropractic


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Cagnie B, et al. Changes In Cerebellar Blood Flow After Manipulation of The Cervical Spine Using Technetium 99m–Ethyl Cysteinate Dimer. J Manipulative Physiol Ther 2005;28:103- 107.

Evidence-based Chiropractic


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Bradford Hill (cont.)

  • When using them, don’t forget Hill’s advice:

    • “None of these nine viewpoints can bring indisputable evidence for or against a cause and effect hypothesis …. What they can do, with greater or less strength, is to help answer the fundamental question—is there any other way of explaining the set of facts before us, is there any other answer equally, or more likely, than cause and effect?” (Cited in Doll, 1991)

Evidence-based Chiropractic


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Smoking causes lung cancer

  • Where is the RCT that gave evidence to this?

  • Decades of observational research

    • Observing the same thing in a wide variety of settings

    • Some free of some types of bias, others free of other types of bias

Evidence-based Chiropractic


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Smoking & lung cancer

  • It takes a lot of observational data to even begin to suggest causation!

    • Strength of association – Consistency – Specificity – Temporality – Biologic gradient (dose/response) – Biologic plausibility – Coherence of evidence

Evidence-based Chiropractic


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Smoking & lung cancer: Example of causality guidelines

  • Cohort studies clearly demonstrate that smoking precedes lung cancer

  • Risk ratios between smoking and lung cancer are high in many studies

  • The more cigarette smoke inhaled over a lifetime, the greater the risk of cancer

Evidence-based Chiropractic


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Example of causality guidelines cont.

  • Association found in both sexes, all races, all strata of socio-economic status (SES), etc.

  • Burning tobacco produces carcinogenic compounds which contact pulmonary tissue

Evidence-based Chiropractic


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Bradford Hill examplesmoking and lung cancer

  • Strength of Association

    • The lung cancer rate for smokers is quite a bit higher than for nonsmokers (e.g., 80% of female and 90% of male lung cancer cases were smokers)

  • Temporality

    • Smoking precedes the onset of lung cancer in the vast majority of cases

Evidence-based Chiropractic


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Bradford Hill example cont.

  • Consistency

    • Different methods produced the same result (e.g., prospective and retrospective studies)

    • The relationship is apparent in different kinds of people (e.g., males and females)

  • Theoretical Plausibility

    • The biological theory of smoking causing tissue damage which over time results in cancer in the cells is highly plausible

Evidence-based Chiropractic


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Bradford Hill example cont.

  • Coherence

    • The conclusion that smoking causes lung cancer makes sense, given the current knowledge about the biology and history of the disease

  • Specificity in the causes

    • Lung cancer is best predicted from among smokers, although there are other causes

Evidence-based Chiropractic


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Bradford Hill example cont.

  • Dose Response Relationship

    • Data shows a positive linear relationship between the amount smoked and the incidence of lung cancer

  • Experimental Evidence

    • Tar painted on laboratory rabbits’ ears produces cancer in the ear tissue over time

    • As a result, it was clear that carcinogens were present in tobacco tar

Evidence-based Chiropractic


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Bradford Hill example cont.

  • Analogy

    • Induced smoking with laboratory rats showed a causal relationship

    • Therefore, it was not a great jump for scientists to apply this to humans

Evidence-based Chiropractic


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Smoking and cirrhosis of the liver?

  • The incidence of cirrhosis of the liver is associated with cigarette smoking. Does this mean smoking causes cirrhosis?

  • Heavy smokers tend to be heavy drinkers, the statistical association is there, but in this case is probably a confounding variable. Excessive consumption of alcohol is a more likely cause.

Evidence-based Chiropractic


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ANNUAL PHYSICAL AND ECONOMIC COST OF MEDICAL INTERVENTION

Death by Medicine Gary Null PhD, Carolyn Dean MD ND, Martin Feldman MD, Debora Rasio MD. October 2003. www.GaryNull.com

Evidence-based Chiropractic


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Aims of epidemiologic research

  • Describe the health status of a population

  • Explain the etiology of disease

  • Predict the disease occurrence

  • Control the disease distribution

Evidence-based Chiropractic


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Epidemiologyis used inclinicalpractice to. . .

  • Describe the natural history of diseases

  • Discuss disease causality

    • Proximate (biological)

    • Distal (social & environmental)

  • Evaluate diagnostic testing

    • Usefulness, sensitivity, specificity

    • Set cutoff points, and develop screening strategies

Evidence-based Chiropractic


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Epidemiologyinclinicalpractice (cont.)

  • Evaluate prognosis

    • by identifying prognostic factors

    • through cohort and case-control studies 

Evidence-based Chiropractic


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Epidemiological reasoning

  • Derive inferences regarding possible causal relationships

  • Determine whether these relationships are spurious or true

  • Discussion:

    • Associations (height & weight)

    • Causal relationships (overeating & weight)

    • Threats to validity (some of group dieting)

    • Play of chance (statistical association)

Evidence-based Chiropractic


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Figure 1. U.S. Mortality Data for Seven Selected Disorders in 1997.

A total of 16,500 patients with rheumatoid arthritis or osteoarthritis died

from the gastrointestinal toxic effects of NSAIDs.

Data are from the National Center for Health Statistics and the Arthritis,

Rheumatism, and Aging Medical Information System.

Evidence-based Chiropractic


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Estimating Risk: is there an association?

  • Compare the risk of outcome in exposed to the risk of outcome in the non-exposed

  • Relative Risk

    • Calculated in cohort studies

    • Prospective

  • Odds Ratio

    • Calculated in case-control studies

    • Retrospective

Evidence-based Chiropractic


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Relative Risk

  • RR=1, risk in exposed equal to risk in non-exposed (no association)

  • RR>1, risk in exposed greater than risk in nonexposed (positive association, possibly causal)

  • RR<1, risk in exposed less than risk in nonexposed (negative association, possibly protective)

Evidence-based Chiropractic


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Sample

  • One is interested in the parameters of a population but, for practical reasons, must estimate them by describing the statistics of a sample

  • A subset of a population

  • Selected from a population

    • 100,000 randomly selected US residents

    • LBP patients recruited for a clinical trial

Evidence-based Chiropractic


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Sample (cont.)

  • Sample statistics are only estimates of the corresponding population quantities because they are computed from a sample selected from the population

  • Therefore, based upon statistics derived from samples, population parameters are estimated

Evidence-based Chiropractic


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Populations and Samples

Evidence-based Chiropractic


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The intended population represented by the sample

  • Simply stated, a population is a group of people in a defined setting or with a certain characteristic

    • The general population

    • Adults with low back pain

    • Residents of North Carolina

    • Members of a California HMO

    • Chiropractic students

  • More to come in EBC 2

Evidence-based Chiropractic


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Sample size . . .

  • Affects the probability of detecting a real difference between groups if there is one

  • In other words, the probability that a difference seen between the groups is real and is not just a random occurrence

    • The sample must be representative of the population

Evidence-based Chiropractic


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Sample size is not happenstance!

  • To draw conclusions about the effectiveness of treatment (i.e. the difference between 2 groups’ outcomes) a RCT must have the statistical power to detect a real difference

  • Sufficient numbers of subjects required to reach statistical significance

  • Often not calculated (77% of the time chiropractic, 83% spine surgery journals)

Evidence-based Chiropractic


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Importance of sample size

  • Drawing conclusions about a population based upon a sample

    • Study says: Group A = Group B

      • Caution - Small numbers increase the chance of a Type II error

      • Saying there isn’t a difference, when there is

    • Study says: Group A ≠ Group B

      • Caution - Small numbers increase the chance of a Type I error

      • Saying there is a difference, when there isn’t

Evidence-based Chiropractic