PLS 210-A01

Scientific method, cont’d

Immunology: 1796 – Smallpox/cowpox discussion — Dr. Edward Jenner: milkmaids with cowpox never got smallpox

declared extinct in 1980’s

Hypothesis: There is a relationship between occupation and susceptibility to smallpox, such that milkmaids are not susceptible but non-milkmaids are.

Essex: poll the barn (hospital for sick milkmaids) for 2 pieces of info: occupation (Milkmaid/Other), susceptible (Y/N) to smallpox

Non-milkmaid Milkmaid
susceptible Y 50 0 50
susceptible N 0 50 50
Totals 50 50 100

Wessex: Same result, apparently confirmed

Non-milkmaid Milkmaid
susceptible Y 50 0 50
susceptible N 0 50 50
Totals 50 50 100

Sussex: Same result, apparently confirmed

Non-milkmaid Milkmaid
susceptible Y 50 0 50
susceptible N 0 50 50
Totals 50 50 100

Nosex table 1: relationship not in expected direction – hypothesis falsified

Non-milkmaid Milkmaid
susceptible Y 0 50 50
susceptible N 50 0 50
Totals 50 50 100

Nosex table 2: no relationship at all – hypothesis falsified

Non-milkmaid Milkmaid
susceptible Y 25 25 50
susceptible N 25 25 50
Totals 50 50 100

Terminology

  • table
  • cross-tabulation
  • contingency table
  • cells
  • grand total
  • marginal total
  • Predictive model
  • association
  • correlation
  • experiments, experimental controls

Induction: verification = if true/confirmation
Deduction: if false/ disconfirmation (falsification)
Theory: 2 or more hypotheses presented as an explanation of some phenomena
Scientific law: theory that is so fully accepted and tested that is no longer in question

2 functions of research: explain or predict

Temporal Sequence:

  1. independent variable: the variable which provides the explanation (occupation, milkmaid)
  2. dependent variable: the variable being explained

NOTE: difference between attributes and quantities/amounts
If both variables are amounts/quantities:

When all variables are amounts: same as tables above, but status and income are variables: high and low for both
simply stated: “income and status are positively related” or “…inversely related”

When one or more variables are attributes, hypothesis statement cannot be so simplified.

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