It’s generally agreed that there are seven basic tools needed to get started in SPC (Statistical Process Control). Some are so basic many people use them without realising they’re getting into statistics (and their link to what we think of as *statistics* often seems quite tenuous)…

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# Category Archives: Probability

# Reliability

A lot is spoken about reliability – it’s a common topic of conversation in the pub or over coffee, often as a result of a bad experience (poor reliability). It’s a term that is relates very much to quality but is possibly easier to define and quantify. Unfortunately, the numbers that come out of any quantification are rarely much comfort when your widget was one of the small percentage of ones to fail. It’s not even as comforting as seeing somebody else win the lottery jackpot: your numbers had the same chance of winning, but didn’t (at least, with the lottery, you’re in the majority). Continue reading

# Control Charts

### Control Charts

Popularised by Deming, control charts recognise that there is variation in every process, the secret to quality is knowing what it is. There are, in fact, two quite distinct types of variation: Continue reading

# Black Swans

Not an ornithological post but a few words about expecting the unexpected – planning for the unknown. Before somebody cries out that if you could expect the unexpected it wouldn’t have been unexpected, I mean: don’t always be so confident about probability predictions.

In Elizabethan England, swans were white – big white birds. A black one? No way! Unheard of; not even thought of – until they were found in Australia. Then they caused a stir – *black* swans – totally unexpected. But, of course, naturalists came to explain how they evolved and they shouldn’t have come as a surprise. Predicting the past is a lot easier than predicting the future… Continue reading

# Risky Steaks

Following on from my previous post on what I see as problems with many risk assessment…

Most businesses I audit use a two-factor risk assessment process, multiplying a severity rating of a consequence by the probability it will happen to reach a value of risk. Whilst many schemes assign numbers to the two factors it’s still a qualitative (or subjective) process – the numbers are no more than a ranking.

# Probability (Part 2) – Confidence

Continuing on the probability theme, I want to touch on confidence – that is, the confidence that a probability (or statistical conclusion) is correct. I’m not going to include equations to calculate confidence limits as they can be found in almost any text book on statistics. Rather, I want to try and draw out an understanding of what “confidence” means in this context because it’s easy to confuse people and make it harder than it should be. Continue reading

# Probability (Part 1)

I expect that most people reading this have studied statistics at some time. You may have gone no further than calculating the arithmetic mean and standard deviation for an arbitrary list of number, or you may have used statistical methods such as Anova, the Student ‘t’ test and looked for confidence limits – you may even have encroached into analysing non-parametric data. Congratulations on wherever you got to but I’m going to go a slightly different way. I’m putting aside the equations, tables and calculators and consider an associated topic – probability. Continue reading