Qualitative and quantitative data: reading graphs, charts and tables

How far can you trust a line that plunges? Suppose a news site runs a story about a chain of games shops, with a line graph of its yearly sales. The line drops from the top of the chart almost to the bottom, and the headline says, "Sales collapse!" Then you look at the numbers up the left-hand side. The axis does not start at zero. It starts at forty-eight million pounds. How big was the fall, really? The answer is in the numbers the headline skipped.

Business data comes in two kinds, and the first question about any piece of it is which kind it is. Quantitative data is numbers that can be counted, measured and compared. Sales figures, prices and the tally from a survey are all quantitative. Qualitative data is words that give opinions, feelings and reasons. A customer's comment in an interview is qualitative, and so is an answer to an open question, one that people answer in their own words. Quantitative data tells a business how many or how much. Qualitative data tells it why. One test sorts them. Ask whether you can count it. If you can, it is quantitative, and if it is opinions or reasons in words, it is qualitative. Now try that test on a gym's data. Which of these is qualitative: the number of members who joined in March, an average visit of forty minutes, or a member saying the changing rooms feel cramped? The comment about the changing rooms is qualitative, because it is an opinion in words. The other two are numbers you can count or measure, so they are quantitative. One examiner's report on a question matching business terms to their meanings records that "some candidates confused qualitative and quantitative data." The fix is the counting test, used every time a question names either kind of data.

Before you read a single value from a table or chart, read its labels, because they tell you what each number counts and in what unit. A table has headings across the top and down the side, and each value sits where a row meets a column. The heading says the unit, such as pounds, units sold or per cent. Charts often shrink big numbers. A label saying thousands means every value is a thousand times what is written, and a label saying millions means a million times. CaseCraft sells phone cases. Its bar chart shows units sold each quarter, a quarter being three months, and the axis label says units sold, in thousands. The bars read eighteen in quarter one, twenty-two in quarter two, twenty-five in quarter three and thirty-one in quarter four. How many more cases did CaseCraft sell in quarter four than in quarter one? Read the label before the bars, then work it out. Step one reads the two bars with their label, so both readings are in thousands of cases. Quarter four is thirty-one thousand and quarter one is eighteen thousand. Thirty-one thousand take away eighteen thousand is thirteen thousand. Carrying the unit gives the answer: CaseCraft sold thirteen thousand more cases in quarter four. An answer of thirteen, with no thousands, is out by a factor of a thousand. Sales rose by more than two thirds through the year, so CaseCraft needs more stock ready for the same quarter next year. One examiner's report on a question with values in thousands says, "The majority of students who were not able to gain full marks did not include either £s or 000s." Those answers left off the pound sign or the thousands. The habit is to read the axis label before the bars, and to write its unit on every line of the answer. Now a quick one on a different unit. A bar on a revenue chart labelled millions of pounds reads two point four. What revenue does it show? It shows two point four million pounds, which is two million four hundred thousand pounds. One more reading habit. When a question asks you to identify or read a value, read it and stop, and calculate only when the question asks you to.

A line chart shows how one figure changes over time, which makes it the chart you read for a trend. A trend is the general direction a set of figures moves in over time. Back to the games shop chain, and this time the axis comes first. It runs from forty-eight million pounds at the bottom to fifty million pounds at the top. The line falls from fifty million pounds in twenty twenty-one to forty-eight point two million in twenty twenty-four. How far did sales fall, from fifty million pounds to forty-eight point two million pounds, in pounds and as a percentage? Fifty million take away forty-eight point two million is one point eight million pounds. Over the original fifty million, times a hundred, that is a fall of three point six per cent. That is a real fall, but it is under four per cent. The line looked like a collapse because the axis started at forty-eight million, so a small dip filled the chart's height. Drawn from zero, the same line would barely move. That is why the axis is the first thing you read on any chart. Describing a trend means saying four things: the direction, the start year with its figure, the end year with its figure, and any dip or turning point on the way. Tidepool Ice Cream's yearly revenue was two hundred and ten thousand pounds in twenty twenty, two hundred and forty-five thousand in twenty twenty-one, and two hundred and ninety thousand in twenty twenty-two. It was two hundred and seventy-five thousand pounds in twenty twenty-three, and three hundred and forty thousand pounds in twenty twenty-four. How would you describe the trend in Tidepool's revenue? Write your sentence with all four parts, then check it against mine. Start with the direction. Across the five years, Tidepool's revenue went up. Then the start and the end. It rose from two hundred and ten thousand pounds in twenty twenty to three hundred and forty thousand pounds in twenty twenty-four. Then the dip, because the rise was not steady. Revenue fell once, from two hundred and ninety thousand pounds in twenty twenty-two to two hundred and seventy-five thousand in twenty twenty-three, before climbing to its highest level. Compare that with "sales are going up", which has no years, no figures and no units. One examiner's report on a trend question says, "Many students failed to use the data in their response and simple statements such as 'the value is increasing' were not awardable." Statements like that earned nothing because they used none of the data. The fix is the four-part sentence: direction, start, end and any dip, each with its year and its figure.

A pie chart shows how a whole splits into parts, with each slice a percentage of the total. Moorland Tea Company asked four hundred customers for their favourite range: fruit teas took forty-five per cent, black teas thirty, green teas fifteen and herbal teas ten. How many of the four hundred customers chose fruit teas, at forty-five per cent? It is a percentage of an amount. Forty-five over a hundred, times four hundred customers, is one hundred and eighty customers. The same survey also collected written comments, such as, "The fruit tea tastes fresher than supermarket brands." Of the pie chart percentages and the written comments, which part of Moorland's survey is quantitative data, which is qualitative, and why? The pie chart percentages are quantitative, because they count how many customers chose each range. The written comments are qualitative, because they give opinions and reasons in words. Together they tell Moorland that fruit tea is the favourite, and one reason why: freshness, which it could use in its advertising. Whether the data comes from market research, a business's accounts or a report on its market, the reading is the same: labels and units first, then the values. One examiner's report notes, "This series examiners saw an increase in the proportion of candidates who calculated data from the graph and used it as part of their response." Working out Moorland's hundred and eighty customers from the pie chart is that habit.

Time to test it, with every question coming to you.

A hotel asks guests to score their stay out of ten, and to write a sentence on what they liked. Which of the two is qualitative? The written sentence is qualitative, because it gives reasons in words. The scores can be counted, so they are quantitative.

Now a table instead of a chart. A shop's costs table is headed pounds, in thousands, and its rent row reads twelve. What is the rent? The rent is twelve thousand pounds, because the heading puts every value in thousands of pounds.

Next comes a pie chart. It shows two hundred survey answers, and one slice is twenty-five per cent. How many answers is that? Twenty-five over a hundred, times two hundred answers, is fifty answers.

Now to finish, what four parts does a trend description need? It needs the direction, the start year with its figure, the end year with its figure, and any dip or turning point.

Back to the games shop headline, rewritten as a trend with its years and figures. Sales fell from fifty million pounds in twenty twenty-one to forty-eight point two million pounds in twenty twenty-four, a fall of under four per cent.

If you're solid on this, give it a thumbs-up, so you know you can leave it. If not, save it, give it a day, and look at it again.

Next in the chapter is Using data to make and justify business decisions. Hopefully that's next in your feed, but if not, search for ScholaFly B U oh two, oh four.

Every other video is on scholafly.com too, easy to search by video code or by keyword. Whatever you're revising, go there and have a look, or, watch the next video.