**SAP results**

0

.08

Mean

.12

.22

0

1

2

3

4

5

6

7

8

9

**MSP results**

0

.08

Mean

.12

.22

0

1

2

3

4

5

6

7

8

9

**Share of last digits**

**Number of registered voters**

0

.08

Mean

.12

.22

0

1

2

3

4

5

6

7

8

9

Figure 2: Frequencies of last digits, Sweden 2002

within a municipality.

The vertical axis gives the statistic of interest. For the ﬁrst graph, it denotes the extent

to which the last and penultimate digits within a given municipality are the same, relative

to the lower conﬁdence bound. Municipalities marked in black above the dashed line at 0

have suspiciously few repetitions. The second graph shows the extent to which digits are

adjacent in a given municipality, relative to the upper conﬁdence bound. Points above 0 have

worryingly many pairs of adjacent digits. The third graph displays the degree to which we

observe pairs of non-neighboring digits, relative to the lower conﬁdence bound. The black

dots indicate municipalities with suspiciously few pairs of non-adjacent digits.

There are a small number of municipalities that are seemingly suspicious, but this is

the result of the fact that we plot unadjusted 95% conﬁdence bounds for a test of many

hypotheses—one for each municipality. Since we plotted just short of 200 municipalities (in

order to facilitate comparison with our analysis of Nigeria’s 2003 election), it is not surprising

that a small number of them will lie beyond the 95% conﬁdence interval purely by chance.

Again, we cannot reject the null hypothesis of a “clean” election.

4.2

Data and results from Nigeria

We now use our digit-based test to examine electoral returns from Nigeria. In particular we

analyze data at the polling station level for Plateau state, which is located in the “middle

belt” region of the country. We were able to retrieve this data in 2006, and it is, to our

knowledge, the ﬁrst time that post-colonial election data at this level of aggregation has been

available outside of Nigeria. The body of data we gathered consists of a nearly complete

record of the 2003 presidential, gubernatorial, and parliamentary elections for Plateau and,

to some extent, neighboring Kaduna state. We here analyze presidential election returns for

Plateau state.

All results were entered from original, handwritten electoral ward report sheets used by

local authorities, and we focus on the ward as our target of analysis. Figure 4 provides an
example of such a ward-level return sheet, highlighting the digits we will analyze below. For

9