• Hi Robert,

    Thank you for your suggestion to look into NIST standards. In fact it appears that NIST are also soliciting for a suitable ‘Airborne Formaldehyde Monitor’ technique.

    Unfortunately the standards I have seen to date (ISO, ASTM etc…[Read more]

  • I wish to establish the variability of a test method to determine formaldehyde emissions from a board. The source of variability may be between different boards (different batches manufactured on different days), within the same board (specimen pieces cut from different locations on the board) or in the test method itself. As I am the only person…[Read more]

  • To begin with I should thank everyone for perservering with my problem and I shall try explain further my work as I now realise I did not provide sufficient background.

    I am developing a new epoxy paint which can be brush or spray applied to grit blasted steel in off-shore structures (oil rigs, wind turbines etc.). Yes the structure was…[Read more]

  • My 8 formulations are essentially the same formulation but with a different additive in each (the control does not contain an additive). To frame my design in DOE terminology; it is best described as one factor with 8 levels. So you can see it is not really a factorial experiment, it is more a traditional experiment to screen a number of different…[Read more]

  • My thanks to everyone who has taken the time to offer advice…


    You raise a valid point, it is essential that I subject each panel to the same contamination procedure. I must admit however that I have just placed all eight panels into a bucket of salt solution (5% by weight). As the water has evaporated I have added further additions…[Read more]

  • Thanks for your help,

    I should have said that the variation in salt contamination is between panels not within the panels. In other words a single panel tested on each of the 4 corners will give pretty consistent readings but the average salt contamination reading for one panel will differ significantly from the next panel.

    The stainless…[Read more]

  • To apply an epoxy coating to an off-shore steel structure, several washes with de-ionised water is required to remove salt contamination from the steel surface. Due to the cost associated with transporting large […] 7 years, 2 months ago

  • Thank you Robert
    7 years, 6 months ago

  • Thank you Robert,

    I like your second suggested approach.

    I am using the ‘Analysis ToolPak’ plug-in on Microsoft Excel.

    My understanding is that my software uses the following t-value in a one tailed t-test…

    t = (slope – 0)/Standard error of slope

    Am I correct in saying that this is the approach you suggested?

    Thank you…[Read more]

  • I have 8 coatings. I have measured the surface energy of each coating then coated the inside wall of a pump with each and measured the increase in pump efficiency.
    In other words I have two sets of paired data, […] 7 years, 6 months ago

  • Thank you Joel,
    I had not considered blocking. Your approach is the one I will go with as it maintains the orthogonal nature of the design while providing a solution to my problem.
    8 years, 4 months ago

  • “How are you going to run a central composite on type variables?”

    Oops! mea culpa, I think I got a bit ahead of myself in that I anticipated my problem regarding 0% silica levels before I’ve had a chance to sit down and think about the appropriate design.

    In fact my plan was to initially do a 2-level factorial design; then if the fa…[Read more]

  • My formulation is a simple mixture of ingredients and I intend to carry out a central composite design to establish optimum level and combination of ingredients. I wish to investigate the following four […] 8 years, 4 months ago

  • Thank you Joel, I see what you are saying. Even if I had many more true values for my first variable it should not concern me as the split on the second variable between true and false will either exhibit dependence or it won’t.

    Robert, you raise an interesting point. A quick Google search on sensitivity and specificity revealed a discussion…[Read more]

  • roarty changed their profile picture 8 years, 7 months ago

  • Hi Robert,

    Thank you for your interest. If I seem a little confused; it’s because I am.

    I think it would help if I gave you a little background. The problem relates to the manufacture of an epoxy composite material. A colleague of mine is tasked with quality control. Once a batch is made he will take a sample of the liquid product add the…[Read more]

  • I just want to make a correction to my original post.

    My degrees of freedom is 2-1 = 1 and not 3 as I first thought. I am interested in if the pairs match, so there are of course only two possible outcomes either they match or they dont.

    The chi-squared test was the best approach – Thanks Darth. As it happens the percentage of ‘TRUE’ values…[Read more]

  • Thanks Darth,

    A bias towards ‘TRUE’ is not necessarily desirable but I fear the data may be skewed in that direction so I guess I should account for it.

    I agree, some common sense is required here, so I shall do the test on both null hypotheses then choose the result that makes sense based on what I know about my system and on how the data l…[Read more]

  • Thanks Darth,

    As you suggest, the Chi-squared test will give me a value to compare against critical values on the chi-squared distribution. This is exactly what I was looking for, thank you.

    There are 4 possible outcomes (True/True, True/False, False/True and False/False) so degrees of freedom; 4 – 1 = 3

    I’m a bit concerned about my n…[Read more]

  • I have two sets of binary data (true/false). The data is paired by date (n = 365) and I wish to express the degree to which the pairs match.
    The simplest approach would be to calculate the percentage of pairs that […] 8 years, 7 months ago

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