Quantitative methods for politics: an introduction

Massimo De Angelis

• “how to lie with statistics”

• Graphs and Charts

• Descriptive Stats

• Measurements and the “invisible”

• Growth rates

• An application: the Political Economy of growth rates.

“how to lie with statistics”• 1954 Darrell Huff's perennially best-selling[1]

introduction to statistics for the general reader. – Correlation does not imply causation

• numerous epidemiological studies showed that women who were taking combined hormone replacement therapy (HRT) were found to have a lower than average incidence of coronary heart disease (CHD), leading doctors to propose that HRT was protective against CHD.

• Controlled trials, however, showed that HRT actually caused a small but significant increase in risk of CHD.

• Re-analysis of the data showed that women undertaking HRT were more likely to be from socio-economic groups ABC1, with better than average diet and exercise regimes. The two were coincident effects of a common cause, rather than cause and effect as had been supposed.[

– Statistical graphs can be used to distort reality:• By truncating the bottom of a line or bar chart, one

makes differences seem larger than they are • By representing one-dimensional quantities on a

pictogram by two- or three-dimensional objects to compare their sizes, one makes the reader forget that the images don't scale the same way the quantities do. Two rows of small images would give a better idea than one small and one big one.

Statement: Carpenters in Country 1 make 1/2 as much as Carpenters in Country 2. The first one is inaccurate and the second one is correct. First Picture doubled the height of the smaller money sack, but then the artist had to make the width larger for the money sacks to be proportional. According to the first picture 4 of the smaller money sacks can fit into the larger one. Therefore Carpenters in Country 1 make 1/4 as much as carpenters in Country 2?

• 100, 100, 99, 98, 96, 95, 92, 90, 89, 73, 70, 10, 10, 10, 10, 9, 9, 8, 8

• Find the • mean => 58.55• median => 81 • mode => 10 • standard deviation => 41.998

– How far on average the variable’s observations are from the variable’s mean.

Basic descriptive stats

}MEASURES OF CENTRAL TENDENCIES

• Standard deviation =

• normal distribution

• Skewness

• Unimodal and multimodal distribution

Index numbers* index numbers are time series summarising movements in a group of related variables. The best-known is the consumer price index which measures changes in retail prices paid by consumers.

•What is included in the CPI?•What is the base year?

Measurement and the “invisible”

• “GDP growth will solve our problems” . . .such as – Reduce poverty– Improve environment . .etc.

• Problem– GDP is a monetised measure of social production

• What activity and who are the excluded from this measure?• GDP per capital (often provided as a measure of “progress”)

is hides income distribution, • See for example http://www.twnside.org.sg/title/2086.htm

http://www.econbrowser.com/archives/2007/01/sachs.png

Rates of Growth

• Rate of growth =

(Change in a variable/Value of variable t0)*100

Bacteria example =>

the Political Economy of growth rates: the productivity deals of post-WWII

From http://homepages.uel.ac.uk/M.DeAngelis/EC213ch6b.doc

P = ProfitW = WagesL = Labour hoursY = Total OutputY = P + Wg(Y/L) = g(P/L) + g(W/L)Or g(P/L) = g(Y/L) – g(W/L)

If g(Y/L) = g(W/L) = g(P/L) same income shares in society

G => indicates growth