MCAT Math and Physics - Reasoning About the Design and Execution of Research

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scientific method

set of steps that defines the appropriate order of events to structure and carry out an experiment; established protocol for transitioning from a question to a new body of knowledge

steps in the scientific method

1. Generate a testable question

2. Gather data and resources

3. Form a hypothesis

4. Collect new data

5. Analyze the data

6. Interpret the data and existing hypothesis

7. Publish

8. Verify results

hypothesis

proposed explanation or proposed answer to our testable question; often in the form of an if–then statement

experimentation

involves manipulating and controlling variables of interest

observation

often involves no changes in the subject’s environment

peer review

evaluation of work by one or more people with similar competencies as the producers of the work

FINER method

method to determine whether the answer to one’s question will add to the body of scientific knowledge in a practical way and within a reasonable time period

FINER Method question

1. feasible?

2. interesting?

3. novel?

4. ethical?

5. relevant?

Basic science research

kind conducted in a laboratory, and not on people; generally the easiest to design because the experimenter has the most control; causal relationship is being examined because the hypothesis generally states a condition and an outcome

control / standard

a method of verifying results; an experiment or observation designed to minimize the effects of variables other than the independent variable

Positive controls

ensure a change in the dependent variable when it is expected

Negative controls

ensure no change in the dependent variable when no change is expected

placebo effect

observed or reported change when an individual is given a sugar pill or sham intervention

independent variable

variable that is manipulated

dependent variable

variable(s) that are measured or observed

causal

If the change in the independent variable always precedes the change in the dependent variable, and the change in the dependent variable does not occur in the absence of the experimental intervention

Accuracy / validity

the ability of an instrument to measure a true value

Precision / reliability

ability of the instrument to read consistently, or within a narrow range

systematic error

affects measurements by the same amount or proportion, provided that a reading is taken the same way each time; affects accuracy but not precision; only an inaccurate tool will introduce bias

random error

causes one measurement to differ slightly from the next; changes precision, not accuracy; accuracy; usually overcome by using a large sample size

human subjects research

systematic, scientific investigation that can be either interventional or observational and involves human beings as research subjects

Randomization

method used to control for differences between subject groups in biomedical research; uses an algorithm to determine the placement of each subject into various experimental groups or controls

blinded (experiment)

do not have information about which group the subject is in

single-blind experiments,

only the patient or assessor is blinded

assessor

the person who makes measurements on the patient or performs subjective evaluations

double-blind experiments

investigator, subject, and assessor all do not know the subject’s group

confounding variable / confounders

variables outside of the independent and dependent variables considered that could affect results

binary variables

variables of two choices

ex. yes v. no, better v. worse

continuous variables

variables that any given number can fulfill, sometimes including fractions, decimals and negatives

ex. amount of weight lost, percent improvement in cardiac output

categorical variables

variable that can take on one of a limited, and usually fixed, number of possible values

ex. state of residence, socioeconomic status

Regression analysis

a set of statistical processes for estimating the relationships between a dependent variable and one or more error-free independent variables; may demonstrate linear, parabolic, exponential, logarithmic, or other relationships

Observational studies

draw on the available data and analyze it

Cohort studies

subjects are sorted into groups based on differences in risk factors and then assessed at various intervals to determine how many subjects in each group had a certain outcome

exposures

risk factors in a correlational study; independent variable

outcome

measured results of a correlational study; dependent variable

Cross-sectional studies

categorize patients into different groups at a single point in time

Case-control studies

identifying the number of subjects with or without a particular outcome, and then look backwards to assess how many subjects in each group had exposure to a particular risk factor

Hill’s criteria (definition)

describe the components of an observed relationship that increase the likelihood of causality in the relationship

Hill’s criteria (list)

1. Temporality: The exposure must occur before the outcome

2. Strength: As more variability in the outcome variable is explained by variability in the study variable, the relationship is more likely to be causal.

3. Dose–response relationship: As the study or independent variable increases, there is a proportional increase in the response.

4. Consistency: The relationship is found to be similar in multiple settings.

5. Plausibility: There is a reasonable mechanism for the independent variable to impact the dependent variable supported by existing literature.

6. Consideration of alternative explanations: If all other plausible explanations have been eliminated, the remaining explanation is more likely.

7. Experiment: If an experiment can be performed, a causal relationship can be determined conclusively.

8. Specificity: The change in the outcome variable is only produced by an associated change in the independent variable.

9. Coherence: The new data and hypothesis are consistent with the current state of scientific knowledge.

correlation

any statistical relationship, whether causal or not, between two random variables or bivariate data

Bias

result of flaws in the data collection phase of an experimental or observational study

Confounding

error during analysis; data may or may not be flawed, but an incorrect relationship is characterized

selection bias

subjects used for the study are not representative of the target population

Detection bias

educated professionals using their knowledge in an inconsistent way

Hawthorne effect / observation bias,

the behavior of study participants is altered simply because they recognize that they are being studied

beneficence

obligation to act in the patient’s best interest

nonmaleficence

obligation to avoid treatments or interventions in which the potential for harm outweighs the potential for benefit

autonomy

responsibility to respect patients’ decisions and choices about their own healthcare

justice

responsibility to treat similar patients with similar care, and to distribute healthcare resources fairly; applies to both the selection of a research topic and the execution of the research; when there is risk associated with a study, it must be fairly distributed so as not to unduly harm any group

Belmont Report

landmark document published by the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research in 1979, delineates the three necessary pillars of research ethics:

1. respect for persons

2. justice

3. (slightly more inclusive version of) beneficence

Respect for persons

the need for honesty between the subject and the researcher, and generally—but not always—prohibits deception; includes the process of informed consent; Confidentiality

informed consent

a patient must be adequately counseled on the procedures, risks and benefits, and goals of a study to make a knowledgeable decision about whether or not to participate in the study without coercive influence

institutional review boards

group that has been formally designated to review and monitor ethical research involving human subjects

Vulnerable persons

require special protections above and beyond those taken with the general population

ex. children, pregnant individuals, and prisoners

Confidentiality

keeping information about subjects secret or private

Tuskegee syphilis experiment

notorious forty-year study (1932–1972) by the United States Public Health Service that was fraught with extreme violations of the ethical principle of respect for persons; considered the primary impetus for the writing of the Belmont Report

African American men living in conditions of poverty were enrolled into a study on the natural progression of syphilis. These men were given sham treatments, barred from accessing appropriate healthcare, and repeatedly deceived by investigators—including the fact that they were never told they had syphilis!

Morally relevant differences

differences between individuals that are considered an appropriate reason to treat them differently

equipoise

a situation in which things are perfectly balanced; one cannot approach research with the knowledge that one treatment is superior to the other or the trial must be stopped because providing an inferior treatment is a net harm

population

complete group of every individual that satisfies the attributes of interest

parameter

Information that is calculated using every person in a population

sample

any group taken from a population that does not include all individuals from the population

statistic

Information about a sample

internal validity

support for causality

external validity / generalizability

samples that are representative of the target population

statistically significant

not the result of random chance

clinical significance

notable or worthwhile change in health status as a result of intervention