The scientific method

The scientific method.

What is the scientific method? A simple example to illustrate….

Over 5000 people were questioned about handedness and age.

The subjects or participants of the handedness study were the people who were questioned The data are their answers to the questions. You obtain data when you measure something systematically – conducting the same measurement on every item in a sample that’ s representative of the population of interest.

Empirical means having to do with data (as distinct from theoretical ) A result is replicable when it is obtained from multiple samples. Many studies in North America and Europe have shown that the proportion of left-handers declines with age An inference is a conclusion drawn from evidence; in this case, researchers inferred that left-handers don’ t live as long as right-handers.

A variable is anything that can vary Changes in independent variables are thought to be the cause of… …changes in dependent variables Here, left-handedness is thought to cause early death This is a hypothesis : a proposed causal relationship among two or more variables.

Hypothesis in the handedness study. Left-handedness Early death Independent variable Dependent variable causes.

Science looks for causal relationships In an experiment , scientists manipulate one or more independent variables and record their effect on a dependent variable The handedness study was observational , not experimental Correlation or association among variables doesn’ t, by itself, prove a causal relation between them.

Left-handedness Accident-proneness Early death. OR….

When scientists collect data, it’ s usually for the purpose of testing hypotheses; if a hypothesis is un testable or un falsifiable (i.e. it would be “supported” by the occurrence of any event that could possibly happen), then it’s bad science Hypotheses are often (but not always) based on theories – a theory , like a hypothesis, proposes causal relationships, but at a more abstract level, and covering a wider range of phenomena (variables) The handedness study was not based on any theory.

A hypothesis can be… deduced from theory ( deductive reasoning = from the general to the specific), or… …based on previously accumulated facts ( inductive reasoning = from the specific to the general), or even… …based solely on intuition (but it still must be testable!) For scientists, evidence adjudicates between rival hypotheses or conjectures (this is very different from the way that litigators treat evidence).

Theories: give us the power to deduce hypotheses about a wide range of phenomena tell us what to look for (what variables to measure) pose puzzles and suggest their solutions serve as guides to empirical discoveries Note the difference from the colloquial or everyday definition of theory as a “ guess ” or a “ hunch ”.

Back to the age/handedness result....

Does the inference (that left-handedness causes early death) depend on any assumptions ? An assumption is a statement accepted as true without evidence Some assumptions are necessary.

And some are quite reasonable, e.g. in this study, the assumption that left-handers are no more likely than right-handers to lie about their age But other assumptions are more questionable, and they too can be tested, just like hypotheses… …such as, in this case, the assumption that no one ever changes from being left-handed to being right-handed.

Is this a valid objection to the handedness study? “ As a left-hander, I find this offensive – it implies that left-handers are inferior – so it must be wrong! ” No – sometimes valid ideas are offensive, e.g. in the 16 th and early 17 th centuries, the belief that the Earth goes around the Sun was highly offensive to many people.

Is it true that left-handers haven’t changed into right-handers? No – one survey (Porac 1996) showed that 80% of left-handers older than 75 (i.e. born before about 1920) remembered an attempt to change them to right-handed in childhood.

If, during the 20 th century, the frequency of forcing left-handed children to change to right-handed declined, this could explain this result (an alternative to the inference that left-handers die younger than right-handers).

From this hypothesis (“forced conversion” of left-handers has declined during the past 80 years) Porac & Friesen (2000) predicted that, for less culturally salient tasks (picking up items), left-hand preference won’t decline with increasing age as it does for writing A prediction is like a hypothesis, but more specific – it includes the way that variables are operationalized.

This prediction was supported by data, which provides support for the hypothesis that “forced conversion” of left-handers declined during the 20 th century So, left-handedness is probably not a cause, or even a correlate, of early death.

How science works – a simplified version:. (Theory) Deduction Hypothesis Deduction Variables operationalized Predictions Deduction Data collection Predictions tested Induction.

Why the scientific method is such a powerful way of gaining knowledge about the world.

Why the scientific method is such a powerful way of gaining knowledge about the world.

big_fat_surprise.tiff. Or at least, that’s how science works in the long run ….