Chapter 12: Data-Based and Statistical reasoning

Question 1

Cohort studies

Answer 1

Cohort studies are those in which subjects are sorted into groups based on differences in risk factors (exposures), and then assessed at various intervals to determine how many subjects in each group had a certain outcome.

Cross-sectional studies attempt to categorize patients into different groups at a single point in time. For example, a study to determine the prevalence of lung cancer in smokers and nonsmokers at a given point in time would be an example of a cross-sectional study.

Case-control studies start by 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. For example, a study in which 100 patients with lung cancer and 100 patients without lung cancer are assessed for their smoking history would be an example of a case–control study.

Question 2

Four ethical tenets

Answer 2

beneficence, or the obligation to act in the
patient’s best interest;

nonmaleficence, or the obligation to avoid treatments or interventions in which the potential for harm outweighs the potential for benefit; respect for

patient autonomy, or the responsibility to respect patients’ decisions and choices about their own healthcare;

and justice, or the responsibility to treat similar patients with similar care,
and to distribute healthcare resources fairly.

Question 3

Internal and External Validity

Answer 3

When analyzing a study, we also look for markers of internal validity (or support for causality as discussed earlier) and external validity, or generalizability.

Studies with low generalizability have very narrow conditions for sample selection that do not reflect the target population, whereas studies with high generalizability have samples that are representative
of the target population.

For example, a psoriasis study with low generalizability might have only participants who were diagnosed within the last year, while a study with high
generalizability would have participants with a distribution of time since diagnosis that is
similar to the population of all psoriatic patients.

Question 4

Skewed distributions

Answer 4

A negatively skewed
distribution has a tail on the left (or negative) side, whereas a positively skewed distribution has a tail on the right (or positive) side.

Because the mean is more susceptible to outliers than the median, the mean of a negatively skewed distribution will be lower than the median, while the mean of a positively skewed distribution will be higher than the median

The direction of skew in a sample is determined by its tail, not the bulk of the
distribution.