graphing trendlines and outliers anomalies n.
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graphing: trendlines and outliers (anomalies). shows points connected (NOT trendlines) suggests there’s a huge dip at 7 minutes this is probably NOT a true picture of the data! the OUTLIER point is probably an error. using trendline usually makes the overall trends clearer .

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Presentation Transcript
slide2

shows points connected (NOT trendlines)

suggests there’s a huge dip at 7 minutes

this is probably NOT a true picture of the data!

the OUTLIER point is probably an error.

slide3

using trendline usually makes the overall trends clearer.

the red trendline gives a better picture of the data than in the previous graph

note there are different KINDS of trendlines

most of the time, we’ll stick with LINEAR trendlines

slide5

orange point is an OUTLIER

  • a point that’s outside of the normal values
  • NOTE IT IN YOUR LAB REPORT
  • try to explain it
  • put it in CONTEXT: this experiment is about pH values
  • note: pH scale only GOES from 0-14!! it would be EXTREMELY ODD to have a change of -18!
  • so this is likely a typo, or misread measurement
  • in which case, it makes SENSE to see what the graph would look like without it
slide7

you can’t just eliminate data.

  • you CAN look at whether it makes any sense.
  • was it an error, or was it some realevent?
      • if error, what caused it?
      • is it even POSSIBLE?
      • if real, why so far off pattern?
  • if it’s an error...
    • how would things look if that point were absent?
slide8

this shows trendline if error is removed

notice it SEEMS a much more reasonable fit

slide10

here’s the same graph with the other lines removed for clarity

  • shows a green linear trendline, AND the join-the-dots line
  • how do the two compare?
  • does the linear trendline show a reasonable picture of the data?
slide11

does the linear trendline seem to be a good fit?

  • if NOT – SUGGEST ALTERNATIVES.
  • SUGGEST WHAT THOSE ALTERNATIVES MIGHT MEAN.
  • does the data level off?
  • if so – why?
  • does the data make a curve? if so, does that make sense?
  • sigmoid curve? parabola?
slide12

maybe it’s a steep rise, and then it levels off... ?

  • does this make sense?
  • this would be a great place to do some background research.
slide13

a linear LOBF ASSUMES that it’s a linear trend!

  • but there are other trends...
  • does your LOBF (trendline) actually represent what’s happening?
  • a good lab report would show it both ways: (a) linear; (b) level-off
  • then EXPLAIN which makes more SENSE under the circumstances