The Craft of Scientific Presentations Summary: Explain Evidence

Key Ideas

1. Choose the speech for the people actually listening

The book identifies giving the wrong speech as a critical error. For a technical presenter, the same work can require different explanations in different rooms. A specialist may need to inspect an experimental choice; a collaborator from another field may first need a reason to care about it. The audience’s task should therefore influence the route through the talk, not just the vocabulary used on the slides.

Lina’s cooling-layout presentation is for a mixed engineering lab group deciding what to test next. She does not start by displaying every instrument specification. She first identifies the practical question and explains the comparison. She retains the measurement detail that lets the group evaluate the observation, with further specifications available for questions. If she were speaking to students learning the apparatus, more of the construction sequence might belong in the main talk.

Before preparing slides, write what the listeners already know and what you want them to understand afterward. Then identify a likely question from someone outside your immediate project. A short conversation with that person can expose a missing definition or an assumption that seems obvious only within the team.

This matters because shortening an unsuitable speech does not make it suitable. The wrong explanation can remain difficult even when the slides are elegant. Check that the intended audience can follow the opening problem before refining the conclusion. Adapting the talk should preserve the work’s substance while providing the context these listeners need to examine it.

2. Build a sequence of messages before opening the template

The assertion-evidence tutorial asks presenters to write their main messages before creating slides. A message is more specific than a topic label. Putting these sentences in order makes it possible to inspect the logic of a talk before its visual surface becomes expensive to change.

For Lina’s invented example, the sequence begins with the reason for comparing the layouts. It then identifies the conditions used in the test, states the observed difference with suitable limits and ends with the question a further experiment should investigate. A heading such as Temperature results becomes a sentence about the particular comparison. The sentence must match whatever observations the eventual real dataset actually supports; it cannot be written to promise a preferred result before analysis.

Lay your proposed messages on separate cards. Ask whether a person could understand why each one follows the previous one. If a card introduces a new variable, define it before relying on it. If a conclusion requires several unsupported leaps, decide whether you need an intermediate explanation or a narrower claim.

This matters because a chronological record and a comprehensible argument serve different purposes. The notebook preserves what happened; the talk helps an audience understand what the work means. Keep material that is necessary for that understanding, and place secondary detail in an accessible supporting document. Do not remove inconvenient evidence simply because it interrupts an attractive sequence. The structure should make the reasoning easier to inspect, including the point where uncertainty remains.

3. Let the visual evidence support the exact assertion

Assertion-evidence design connects a sentence headline with visual support. That pairing creates a useful revision question: can a listener see why this particular evidence belongs under this particular claim? A related image or an impressive technical drawing may attract attention without providing that support. The speaker must also explain what to look at and how to interpret it.

In Lina’s example, a photograph establishes the arrangement of the apparatus, while a plot would be needed to show the measured comparison. Those visuals do different jobs. She does not put the apparatus photograph beneath a claim about comparative performance and expect it to establish the result. If a plot is used, its axes, units, conditions and uncertainty notation need to be readable and explained. A comparison that depends on a restricted operating range should retain that restriction in the assertion or its immediate context.

Take a draft slide and hide the headline. Ask what conclusion the visual supports. Then hide the visual and ask what kind of evidence the headline requires. A mismatch is a reason to revise the claim, improve the evidence or divide the explanation into separate moments.

This matters because the appearance of evidence can be mistaken for the substance of an argument. A technical diagram demonstrates that a system has been described; it does not automatically demonstrate that the system performs as claimed. Build the slide around the relationship you need listeners to inspect, and keep an identifiable source for visuals that come from someone else’s work.

4. Make scientific qualifications part of the message

The assertion-evidence approach calls for a clear assertion, but a clear assertion can include conditions and uncertainty. In this guide’s scientific application, precision means stating the strongest message the evidence supports without silently adding a causal explanation or generalizing beyond the study. This is an editorial discipline for using the method, not a separate rule named in the book.

Lina distinguishes three kinds of statements in her preparation notes. One describes an observed difference within the tested setup. Another proposes a possible reason for it. A third recommends what to test next. These are different claims and need different support. A limited comparison between two layouts would not, by itself, show that either layout works best under every operating condition. Nor would a diagram of a possible mechanism establish that the mechanism caused the observation.

Ask a colleague to underline the verbs in each headline. Does the language say that the experiment observed, suggests, demonstrates or proves something? Check whether that strength is justified. Retain relevant conditions close to the claim instead of relegating every limitation to a final slide that people may never see.

This matters because listeners may remember the assertion without the spoken caveat. If the conclusion is preliminary, communicate that status directly and explain what additional evidence would change your confidence. You can still offer a useful next step. A precise account of what remains unknown helps the audience evaluate the work and decide which question is worth pursuing next.

5. Rehearse the explanation, transitions and response to questions

Alley’s Engineering Ambassadors guidance connects practice with explaining visual evidence instead of reading bullets. Rehearsal should therefore test what the audience hears and sees together. A clean deck can expose a preparation gap if the presenter has removed a script without learning how to explain the evidence.

Lina practices describing the apparatus without looking back at a paragraph on the screen. She explains the measurement before interpreting the plot and says the important conditions aloud. At each transition, she makes clear why the next visual is needed. A colleague interrupts with a realistic question about a condition the test did not cover. Lina practices stating that limit and explaining where a follow-up would begin rather than improvising a result.

Record a rehearsal or ask someone to note the exact point where they lose the thread. Check whether a pointer, annotation or pause would make an important relationship easier to follow. Test the presentation in the display format available for the actual talk, and prepare a usable backup for a visual that may fail.

This matters because confidence has a practical basis in familiarity with both the message and the act of explaining it. It does not require memorizing identical sentences or pretending that questions cannot surprise you. Practice a direct response when you do not know, then return to the main reasoning. Aim to make the evidence understandable enough that the audience can ask an informed question about it.